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Diffstat (limited to 'library/alloc/src/collections/binary_heap/mod.rs')
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diff --git a/library/alloc/src/collections/binary_heap/mod.rs b/library/alloc/src/collections/binary_heap/mod.rs new file mode 100644 index 000000000..0b73b1af4 --- /dev/null +++ b/library/alloc/src/collections/binary_heap/mod.rs @@ -0,0 +1,1766 @@ +//! A priority queue implemented with a binary heap. +//! +//! Insertion and popping the largest element have *O*(log(*n*)) time complexity. +//! Checking the largest element is *O*(1). Converting a vector to a binary heap +//! can be done in-place, and has *O*(*n*) complexity. A binary heap can also be +//! converted to a sorted vector in-place, allowing it to be used for an *O*(*n* * log(*n*)) +//! in-place heapsort. +//! +//! # Examples +//! +//! This is a larger example that implements [Dijkstra's algorithm][dijkstra] +//! to solve the [shortest path problem][sssp] on a [directed graph][dir_graph]. +//! It shows how to use [`BinaryHeap`] with custom types. +//! +//! [dijkstra]: https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm +//! [sssp]: https://en.wikipedia.org/wiki/Shortest_path_problem +//! [dir_graph]: https://en.wikipedia.org/wiki/Directed_graph +//! +//! ``` +//! use std::cmp::Ordering; +//! use std::collections::BinaryHeap; +//! +//! #[derive(Copy, Clone, Eq, PartialEq)] +//! struct State { +//! cost: usize, +//! position: usize, +//! } +//! +//! // The priority queue depends on `Ord`. +//! // Explicitly implement the trait so the queue becomes a min-heap +//! // instead of a max-heap. +//! impl Ord for State { +//! fn cmp(&self, other: &Self) -> Ordering { +//! // Notice that the we flip the ordering on costs. +//! // In case of a tie we compare positions - this step is necessary +//! // to make implementations of `PartialEq` and `Ord` consistent. +//! other.cost.cmp(&self.cost) +//! .then_with(|| self.position.cmp(&other.position)) +//! } +//! } +//! +//! // `PartialOrd` needs to be implemented as well. +//! impl PartialOrd for State { +//! fn partial_cmp(&self, other: &Self) -> Option<Ordering> { +//! Some(self.cmp(other)) +//! } +//! } +//! +//! // Each node is represented as a `usize`, for a shorter implementation. +//! struct Edge { +//! node: usize, +//! cost: usize, +//! } +//! +//! // Dijkstra's shortest path algorithm. +//! +//! // Start at `start` and use `dist` to track the current shortest distance +//! // to each node. This implementation isn't memory-efficient as it may leave duplicate +//! // nodes in the queue. It also uses `usize::MAX` as a sentinel value, +//! // for a simpler implementation. +//! fn shortest_path(adj_list: &Vec<Vec<Edge>>, start: usize, goal: usize) -> Option<usize> { +//! // dist[node] = current shortest distance from `start` to `node` +//! let mut dist: Vec<_> = (0..adj_list.len()).map(|_| usize::MAX).collect(); +//! +//! let mut heap = BinaryHeap::new(); +//! +//! // We're at `start`, with a zero cost +//! dist[start] = 0; +//! heap.push(State { cost: 0, position: start }); +//! +//! // Examine the frontier with lower cost nodes first (min-heap) +//! while let Some(State { cost, position }) = heap.pop() { +//! // Alternatively we could have continued to find all shortest paths +//! if position == goal { return Some(cost); } +//! +//! // Important as we may have already found a better way +//! if cost > dist[position] { continue; } +//! +//! // For each node we can reach, see if we can find a way with +//! // a lower cost going through this node +//! for edge in &adj_list[position] { +//! let next = State { cost: cost + edge.cost, position: edge.node }; +//! +//! // If so, add it to the frontier and continue +//! if next.cost < dist[next.position] { +//! heap.push(next); +//! // Relaxation, we have now found a better way +//! dist[next.position] = next.cost; +//! } +//! } +//! } +//! +//! // Goal not reachable +//! None +//! } +//! +//! fn main() { +//! // This is the directed graph we're going to use. +//! // The node numbers correspond to the different states, +//! // and the edge weights symbolize the cost of moving +//! // from one node to another. +//! // Note that the edges are one-way. +//! // +//! // 7 +//! // +-----------------+ +//! // | | +//! // v 1 2 | 2 +//! // 0 -----> 1 -----> 3 ---> 4 +//! // | ^ ^ ^ +//! // | | 1 | | +//! // | | | 3 | 1 +//! // +------> 2 -------+ | +//! // 10 | | +//! // +---------------+ +//! // +//! // The graph is represented as an adjacency list where each index, +//! // corresponding to a node value, has a list of outgoing edges. +//! // Chosen for its efficiency. +//! let graph = vec![ +//! // Node 0 +//! vec![Edge { node: 2, cost: 10 }, +//! Edge { node: 1, cost: 1 }], +//! // Node 1 +//! vec![Edge { node: 3, cost: 2 }], +//! // Node 2 +//! vec![Edge { node: 1, cost: 1 }, +//! Edge { node: 3, cost: 3 }, +//! Edge { node: 4, cost: 1 }], +//! // Node 3 +//! vec![Edge { node: 0, cost: 7 }, +//! Edge { node: 4, cost: 2 }], +//! // Node 4 +//! vec![]]; +//! +//! assert_eq!(shortest_path(&graph, 0, 1), Some(1)); +//! assert_eq!(shortest_path(&graph, 0, 3), Some(3)); +//! assert_eq!(shortest_path(&graph, 3, 0), Some(7)); +//! assert_eq!(shortest_path(&graph, 0, 4), Some(5)); +//! assert_eq!(shortest_path(&graph, 4, 0), None); +//! } +//! ``` + +#![allow(missing_docs)] +#![stable(feature = "rust1", since = "1.0.0")] + +use core::fmt; +use core::iter::{FromIterator, FusedIterator, InPlaceIterable, SourceIter, TrustedLen}; +use core::mem::{self, swap, ManuallyDrop}; +use core::num::NonZeroUsize; +use core::ops::{Deref, DerefMut}; +use core::ptr; + +use crate::collections::TryReserveError; +use crate::slice; +use crate::vec::{self, AsVecIntoIter, Vec}; + +use super::SpecExtend; + +#[cfg(test)] +mod tests; + +/// A priority queue implemented with a binary heap. +/// +/// This will be a max-heap. +/// +/// It is a logic error for an item to be modified in such a way that the +/// item's ordering relative to any other item, as determined by the [`Ord`] +/// trait, changes while it is in the heap. This is normally only possible +/// through interior mutability, global state, I/O, or unsafe code. The +/// behavior resulting from such a logic error is not specified, but will +/// be encapsulated to the `BinaryHeap` that observed the logic error and not +/// result in undefined behavior. This could include panics, incorrect results, +/// aborts, memory leaks, and non-termination. +/// +/// As long as no elements change their relative order while being in the heap +/// as described above, the API of `BinaryHeap` guarantees that the heap +/// invariant remains intact i.e. its methods all behave as documented. For +/// example if a method is documented as iterating in sorted order, that's +/// guaranteed to work as long as elements in the heap have not changed order, +/// even in the presence of closures getting unwinded out of, iterators getting +/// leaked, and similar foolishness. +/// +/// # Examples +/// +/// ``` +/// use std::collections::BinaryHeap; +/// +/// // Type inference lets us omit an explicit type signature (which +/// // would be `BinaryHeap<i32>` in this example). +/// let mut heap = BinaryHeap::new(); +/// +/// // We can use peek to look at the next item in the heap. In this case, +/// // there's no items in there yet so we get None. +/// assert_eq!(heap.peek(), None); +/// +/// // Let's add some scores... +/// heap.push(1); +/// heap.push(5); +/// heap.push(2); +/// +/// // Now peek shows the most important item in the heap. +/// assert_eq!(heap.peek(), Some(&5)); +/// +/// // We can check the length of a heap. +/// assert_eq!(heap.len(), 3); +/// +/// // We can iterate over the items in the heap, although they are returned in +/// // a random order. +/// for x in &heap { +/// println!("{x}"); +/// } +/// +/// // If we instead pop these scores, they should come back in order. +/// assert_eq!(heap.pop(), Some(5)); +/// assert_eq!(heap.pop(), Some(2)); +/// assert_eq!(heap.pop(), Some(1)); +/// assert_eq!(heap.pop(), None); +/// +/// // We can clear the heap of any remaining items. +/// heap.clear(); +/// +/// // The heap should now be empty. +/// assert!(heap.is_empty()) +/// ``` +/// +/// A `BinaryHeap` with a known list of items can be initialized from an array: +/// +/// ``` +/// use std::collections::BinaryHeap; +/// +/// let heap = BinaryHeap::from([1, 5, 2]); +/// ``` +/// +/// ## Min-heap +/// +/// Either [`core::cmp::Reverse`] or a custom [`Ord`] implementation can be used to +/// make `BinaryHeap` a min-heap. This makes `heap.pop()` return the smallest +/// value instead of the greatest one. +/// +/// ``` +/// use std::collections::BinaryHeap; +/// use std::cmp::Reverse; +/// +/// let mut heap = BinaryHeap::new(); +/// +/// // Wrap values in `Reverse` +/// heap.push(Reverse(1)); +/// heap.push(Reverse(5)); +/// heap.push(Reverse(2)); +/// +/// // If we pop these scores now, they should come back in the reverse order. +/// assert_eq!(heap.pop(), Some(Reverse(1))); +/// assert_eq!(heap.pop(), Some(Reverse(2))); +/// assert_eq!(heap.pop(), Some(Reverse(5))); +/// assert_eq!(heap.pop(), None); +/// ``` +/// +/// # Time complexity +/// +/// | [push] | [pop] | [peek]/[peek\_mut] | +/// |---------|---------------|--------------------| +/// | *O*(1)~ | *O*(log(*n*)) | *O*(1) | +/// +/// The value for `push` is an expected cost; the method documentation gives a +/// more detailed analysis. +/// +/// [`core::cmp::Reverse`]: core::cmp::Reverse +/// [`Ord`]: core::cmp::Ord +/// [`Cell`]: core::cell::Cell +/// [`RefCell`]: core::cell::RefCell +/// [push]: BinaryHeap::push +/// [pop]: BinaryHeap::pop +/// [peek]: BinaryHeap::peek +/// [peek\_mut]: BinaryHeap::peek_mut +#[stable(feature = "rust1", since = "1.0.0")] +#[cfg_attr(not(test), rustc_diagnostic_item = "BinaryHeap")] +pub struct BinaryHeap<T> { + data: Vec<T>, +} + +/// Structure wrapping a mutable reference to the greatest item on a +/// `BinaryHeap`. +/// +/// This `struct` is created by the [`peek_mut`] method on [`BinaryHeap`]. See +/// its documentation for more. +/// +/// [`peek_mut`]: BinaryHeap::peek_mut +#[stable(feature = "binary_heap_peek_mut", since = "1.12.0")] +pub struct PeekMut<'a, T: 'a + Ord> { + heap: &'a mut BinaryHeap<T>, + // If a set_len + sift_down are required, this is Some. If a &mut T has not + // yet been exposed to peek_mut()'s caller, it's None. + original_len: Option<NonZeroUsize>, +} + +#[stable(feature = "collection_debug", since = "1.17.0")] +impl<T: Ord + fmt::Debug> fmt::Debug for PeekMut<'_, T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_tuple("PeekMut").field(&self.heap.data[0]).finish() + } +} + +#[stable(feature = "binary_heap_peek_mut", since = "1.12.0")] +impl<T: Ord> Drop for PeekMut<'_, T> { + fn drop(&mut self) { + if let Some(original_len) = self.original_len { + // SAFETY: That's how many elements were in the Vec at the time of + // the PeekMut::deref_mut call, and therefore also at the time of + // the BinaryHeap::peek_mut call. Since the PeekMut did not end up + // getting leaked, we are now undoing the leak amplification that + // the DerefMut prepared for. + unsafe { self.heap.data.set_len(original_len.get()) }; + + // SAFETY: PeekMut is only instantiated for non-empty heaps. + unsafe { self.heap.sift_down(0) }; + } + } +} + +#[stable(feature = "binary_heap_peek_mut", since = "1.12.0")] +impl<T: Ord> Deref for PeekMut<'_, T> { + type Target = T; + fn deref(&self) -> &T { + debug_assert!(!self.heap.is_empty()); + // SAFE: PeekMut is only instantiated for non-empty heaps + unsafe { self.heap.data.get_unchecked(0) } + } +} + +#[stable(feature = "binary_heap_peek_mut", since = "1.12.0")] +impl<T: Ord> DerefMut for PeekMut<'_, T> { + fn deref_mut(&mut self) -> &mut T { + debug_assert!(!self.heap.is_empty()); + + let len = self.heap.len(); + if len > 1 { + // Here we preemptively leak all the rest of the underlying vector + // after the currently max element. If the caller mutates the &mut T + // we're about to give them, and then leaks the PeekMut, all these + // elements will remain leaked. If they don't leak the PeekMut, then + // either Drop or PeekMut::pop will un-leak the vector elements. + // + // This is technique is described throughout several other places in + // the standard library as "leak amplification". + unsafe { + // SAFETY: len > 1 so len != 0. + self.original_len = Some(NonZeroUsize::new_unchecked(len)); + // SAFETY: len > 1 so all this does for now is leak elements, + // which is safe. + self.heap.data.set_len(1); + } + } + + // SAFE: PeekMut is only instantiated for non-empty heaps + unsafe { self.heap.data.get_unchecked_mut(0) } + } +} + +impl<'a, T: Ord> PeekMut<'a, T> { + /// Removes the peeked value from the heap and returns it. + #[stable(feature = "binary_heap_peek_mut_pop", since = "1.18.0")] + pub fn pop(mut this: PeekMut<'a, T>) -> T { + if let Some(original_len) = this.original_len.take() { + // SAFETY: This is how many elements were in the Vec at the time of + // the BinaryHeap::peek_mut call. + unsafe { this.heap.data.set_len(original_len.get()) }; + + // Unlike in Drop, here we don't also need to do a sift_down even if + // the caller could've mutated the element. It is removed from the + // heap on the next line and pop() is not sensitive to its value. + } + this.heap.pop().unwrap() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Clone> Clone for BinaryHeap<T> { + fn clone(&self) -> Self { + BinaryHeap { data: self.data.clone() } + } + + fn clone_from(&mut self, source: &Self) { + self.data.clone_from(&source.data); + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Ord> Default for BinaryHeap<T> { + /// Creates an empty `BinaryHeap<T>`. + #[inline] + fn default() -> BinaryHeap<T> { + BinaryHeap::new() + } +} + +#[stable(feature = "binaryheap_debug", since = "1.4.0")] +impl<T: fmt::Debug> fmt::Debug for BinaryHeap<T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_list().entries(self.iter()).finish() + } +} + +impl<T: Ord> BinaryHeap<T> { + /// Creates an empty `BinaryHeap` as a max-heap. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let mut heap = BinaryHeap::new(); + /// heap.push(4); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[must_use] + pub fn new() -> BinaryHeap<T> { + BinaryHeap { data: vec![] } + } + + /// Creates an empty `BinaryHeap` with at least the specified capacity. + /// + /// The binary heap will be able to hold at least `capacity` elements without + /// reallocating. This method is allowed to allocate for more elements than + /// `capacity`. If `capacity` is 0, the binary heap will not allocate. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let mut heap = BinaryHeap::with_capacity(10); + /// heap.push(4); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + #[must_use] + pub fn with_capacity(capacity: usize) -> BinaryHeap<T> { + BinaryHeap { data: Vec::with_capacity(capacity) } + } + + /// Returns a mutable reference to the greatest item in the binary heap, or + /// `None` if it is empty. + /// + /// Note: If the `PeekMut` value is leaked, some heap elements might get + /// leaked along with it, but the remaining elements will remain a valid + /// heap. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let mut heap = BinaryHeap::new(); + /// assert!(heap.peek_mut().is_none()); + /// + /// heap.push(1); + /// heap.push(5); + /// heap.push(2); + /// { + /// let mut val = heap.peek_mut().unwrap(); + /// *val = 0; + /// } + /// assert_eq!(heap.peek(), Some(&2)); + /// ``` + /// + /// # Time complexity + /// + /// If the item is modified then the worst case time complexity is *O*(log(*n*)), + /// otherwise it's *O*(1). + #[stable(feature = "binary_heap_peek_mut", since = "1.12.0")] + pub fn peek_mut(&mut self) -> Option<PeekMut<'_, T>> { + if self.is_empty() { None } else { Some(PeekMut { heap: self, original_len: None }) } + } + + /// Removes the greatest item from the binary heap and returns it, or `None` if it + /// is empty. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let mut heap = BinaryHeap::from([1, 3]); + /// + /// assert_eq!(heap.pop(), Some(3)); + /// assert_eq!(heap.pop(), Some(1)); + /// assert_eq!(heap.pop(), None); + /// ``` + /// + /// # Time complexity + /// + /// The worst case cost of `pop` on a heap containing *n* elements is *O*(log(*n*)). + #[stable(feature = "rust1", since = "1.0.0")] + pub fn pop(&mut self) -> Option<T> { + self.data.pop().map(|mut item| { + if !self.is_empty() { + swap(&mut item, &mut self.data[0]); + // SAFETY: !self.is_empty() means that self.len() > 0 + unsafe { self.sift_down_to_bottom(0) }; + } + item + }) + } + + /// Pushes an item onto the binary heap. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let mut heap = BinaryHeap::new(); + /// heap.push(3); + /// heap.push(5); + /// heap.push(1); + /// + /// assert_eq!(heap.len(), 3); + /// assert_eq!(heap.peek(), Some(&5)); + /// ``` + /// + /// # Time complexity + /// + /// The expected cost of `push`, averaged over every possible ordering of + /// the elements being pushed, and over a sufficiently large number of + /// pushes, is *O*(1). This is the most meaningful cost metric when pushing + /// elements that are *not* already in any sorted pattern. + /// + /// The time complexity degrades if elements are pushed in predominantly + /// ascending order. In the worst case, elements are pushed in ascending + /// sorted order and the amortized cost per push is *O*(log(*n*)) against a heap + /// containing *n* elements. + /// + /// The worst case cost of a *single* call to `push` is *O*(*n*). The worst case + /// occurs when capacity is exhausted and needs a resize. The resize cost + /// has been amortized in the previous figures. + #[stable(feature = "rust1", since = "1.0.0")] + pub fn push(&mut self, item: T) { + let old_len = self.len(); + self.data.push(item); + // SAFETY: Since we pushed a new item it means that + // old_len = self.len() - 1 < self.len() + unsafe { self.sift_up(0, old_len) }; + } + + /// Consumes the `BinaryHeap` and returns a vector in sorted + /// (ascending) order. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// + /// let mut heap = BinaryHeap::from([1, 2, 4, 5, 7]); + /// heap.push(6); + /// heap.push(3); + /// + /// let vec = heap.into_sorted_vec(); + /// assert_eq!(vec, [1, 2, 3, 4, 5, 6, 7]); + /// ``` + #[must_use = "`self` will be dropped if the result is not used"] + #[stable(feature = "binary_heap_extras_15", since = "1.5.0")] + pub fn into_sorted_vec(mut self) -> Vec<T> { + let mut end = self.len(); + while end > 1 { + end -= 1; + // SAFETY: `end` goes from `self.len() - 1` to 1 (both included), + // so it's always a valid index to access. + // It is safe to access index 0 (i.e. `ptr`), because + // 1 <= end < self.len(), which means self.len() >= 2. + unsafe { + let ptr = self.data.as_mut_ptr(); + ptr::swap(ptr, ptr.add(end)); + } + // SAFETY: `end` goes from `self.len() - 1` to 1 (both included) so: + // 0 < 1 <= end <= self.len() - 1 < self.len() + // Which means 0 < end and end < self.len(). + unsafe { self.sift_down_range(0, end) }; + } + self.into_vec() + } + + // The implementations of sift_up and sift_down use unsafe blocks in + // order to move an element out of the vector (leaving behind a + // hole), shift along the others and move the removed element back into the + // vector at the final location of the hole. + // The `Hole` type is used to represent this, and make sure + // the hole is filled back at the end of its scope, even on panic. + // Using a hole reduces the constant factor compared to using swaps, + // which involves twice as many moves. + + /// # Safety + /// + /// The caller must guarantee that `pos < self.len()`. + unsafe fn sift_up(&mut self, start: usize, pos: usize) -> usize { + // Take out the value at `pos` and create a hole. + // SAFETY: The caller guarantees that pos < self.len() + let mut hole = unsafe { Hole::new(&mut self.data, pos) }; + + while hole.pos() > start { + let parent = (hole.pos() - 1) / 2; + + // SAFETY: hole.pos() > start >= 0, which means hole.pos() > 0 + // and so hole.pos() - 1 can't underflow. + // This guarantees that parent < hole.pos() so + // it's a valid index and also != hole.pos(). + if hole.element() <= unsafe { hole.get(parent) } { + break; + } + + // SAFETY: Same as above + unsafe { hole.move_to(parent) }; + } + + hole.pos() + } + + /// Take an element at `pos` and move it down the heap, + /// while its children are larger. + /// + /// # Safety + /// + /// The caller must guarantee that `pos < end <= self.len()`. + unsafe fn sift_down_range(&mut self, pos: usize, end: usize) { + // SAFETY: The caller guarantees that pos < end <= self.len(). + let mut hole = unsafe { Hole::new(&mut self.data, pos) }; + let mut child = 2 * hole.pos() + 1; + + // Loop invariant: child == 2 * hole.pos() + 1. + while child <= end.saturating_sub(2) { + // compare with the greater of the two children + // SAFETY: child < end - 1 < self.len() and + // child + 1 < end <= self.len(), so they're valid indexes. + // child == 2 * hole.pos() + 1 != hole.pos() and + // child + 1 == 2 * hole.pos() + 2 != hole.pos(). + // FIXME: 2 * hole.pos() + 1 or 2 * hole.pos() + 2 could overflow + // if T is a ZST + child += unsafe { hole.get(child) <= hole.get(child + 1) } as usize; + + // if we are already in order, stop. + // SAFETY: child is now either the old child or the old child+1 + // We already proven that both are < self.len() and != hole.pos() + if hole.element() >= unsafe { hole.get(child) } { + return; + } + + // SAFETY: same as above. + unsafe { hole.move_to(child) }; + child = 2 * hole.pos() + 1; + } + + // SAFETY: && short circuit, which means that in the + // second condition it's already true that child == end - 1 < self.len(). + if child == end - 1 && hole.element() < unsafe { hole.get(child) } { + // SAFETY: child is already proven to be a valid index and + // child == 2 * hole.pos() + 1 != hole.pos(). + unsafe { hole.move_to(child) }; + } + } + + /// # Safety + /// + /// The caller must guarantee that `pos < self.len()`. + unsafe fn sift_down(&mut self, pos: usize) { + let len = self.len(); + // SAFETY: pos < len is guaranteed by the caller and + // obviously len = self.len() <= self.len(). + unsafe { self.sift_down_range(pos, len) }; + } + + /// Take an element at `pos` and move it all the way down the heap, + /// then sift it up to its position. + /// + /// Note: This is faster when the element is known to be large / should + /// be closer to the bottom. + /// + /// # Safety + /// + /// The caller must guarantee that `pos < self.len()`. + unsafe fn sift_down_to_bottom(&mut self, mut pos: usize) { + let end = self.len(); + let start = pos; + + // SAFETY: The caller guarantees that pos < self.len(). + let mut hole = unsafe { Hole::new(&mut self.data, pos) }; + let mut child = 2 * hole.pos() + 1; + + // Loop invariant: child == 2 * hole.pos() + 1. + while child <= end.saturating_sub(2) { + // SAFETY: child < end - 1 < self.len() and + // child + 1 < end <= self.len(), so they're valid indexes. + // child == 2 * hole.pos() + 1 != hole.pos() and + // child + 1 == 2 * hole.pos() + 2 != hole.pos(). + // FIXME: 2 * hole.pos() + 1 or 2 * hole.pos() + 2 could overflow + // if T is a ZST + child += unsafe { hole.get(child) <= hole.get(child + 1) } as usize; + + // SAFETY: Same as above + unsafe { hole.move_to(child) }; + child = 2 * hole.pos() + 1; + } + + if child == end - 1 { + // SAFETY: child == end - 1 < self.len(), so it's a valid index + // and child == 2 * hole.pos() + 1 != hole.pos(). + unsafe { hole.move_to(child) }; + } + pos = hole.pos(); + drop(hole); + + // SAFETY: pos is the position in the hole and was already proven + // to be a valid index. + unsafe { self.sift_up(start, pos) }; + } + + /// Rebuild assuming data[0..start] is still a proper heap. + fn rebuild_tail(&mut self, start: usize) { + if start == self.len() { + return; + } + + let tail_len = self.len() - start; + + #[inline(always)] + fn log2_fast(x: usize) -> usize { + (usize::BITS - x.leading_zeros() - 1) as usize + } + + // `rebuild` takes O(self.len()) operations + // and about 2 * self.len() comparisons in the worst case + // while repeating `sift_up` takes O(tail_len * log(start)) operations + // and about 1 * tail_len * log_2(start) comparisons in the worst case, + // assuming start >= tail_len. For larger heaps, the crossover point + // no longer follows this reasoning and was determined empirically. + let better_to_rebuild = if start < tail_len { + true + } else if self.len() <= 2048 { + 2 * self.len() < tail_len * log2_fast(start) + } else { + 2 * self.len() < tail_len * 11 + }; + + if better_to_rebuild { + self.rebuild(); + } else { + for i in start..self.len() { + // SAFETY: The index `i` is always less than self.len(). + unsafe { self.sift_up(0, i) }; + } + } + } + + fn rebuild(&mut self) { + let mut n = self.len() / 2; + while n > 0 { + n -= 1; + // SAFETY: n starts from self.len() / 2 and goes down to 0. + // The only case when !(n < self.len()) is if + // self.len() == 0, but it's ruled out by the loop condition. + unsafe { self.sift_down(n) }; + } + } + + /// Moves all the elements of `other` into `self`, leaving `other` empty. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// + /// let mut a = BinaryHeap::from([-10, 1, 2, 3, 3]); + /// let mut b = BinaryHeap::from([-20, 5, 43]); + /// + /// a.append(&mut b); + /// + /// assert_eq!(a.into_sorted_vec(), [-20, -10, 1, 2, 3, 3, 5, 43]); + /// assert!(b.is_empty()); + /// ``` + #[stable(feature = "binary_heap_append", since = "1.11.0")] + pub fn append(&mut self, other: &mut Self) { + if self.len() < other.len() { + swap(self, other); + } + + let start = self.data.len(); + + self.data.append(&mut other.data); + + self.rebuild_tail(start); + } + + /// Clears the binary heap, returning an iterator over the removed elements + /// in heap order. If the iterator is dropped before being fully consumed, + /// it drops the remaining elements in heap order. + /// + /// The returned iterator keeps a mutable borrow on the heap to optimize + /// its implementation. + /// + /// Note: + /// * `.drain_sorted()` is *O*(*n* \* log(*n*)); much slower than `.drain()`. + /// You should use the latter for most cases. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// #![feature(binary_heap_drain_sorted)] + /// use std::collections::BinaryHeap; + /// + /// let mut heap = BinaryHeap::from([1, 2, 3, 4, 5]); + /// assert_eq!(heap.len(), 5); + /// + /// drop(heap.drain_sorted()); // removes all elements in heap order + /// assert_eq!(heap.len(), 0); + /// ``` + #[inline] + #[unstable(feature = "binary_heap_drain_sorted", issue = "59278")] + pub fn drain_sorted(&mut self) -> DrainSorted<'_, T> { + DrainSorted { inner: self } + } + + /// Retains only the elements specified by the predicate. + /// + /// In other words, remove all elements `e` for which `f(&e)` returns + /// `false`. The elements are visited in unsorted (and unspecified) order. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// #![feature(binary_heap_retain)] + /// use std::collections::BinaryHeap; + /// + /// let mut heap = BinaryHeap::from([-10, -5, 1, 2, 4, 13]); + /// + /// heap.retain(|x| x % 2 == 0); // only keep even numbers + /// + /// assert_eq!(heap.into_sorted_vec(), [-10, 2, 4]) + /// ``` + #[unstable(feature = "binary_heap_retain", issue = "71503")] + pub fn retain<F>(&mut self, mut f: F) + where + F: FnMut(&T) -> bool, + { + let mut first_removed = self.len(); + let mut i = 0; + self.data.retain(|e| { + let keep = f(e); + if !keep && i < first_removed { + first_removed = i; + } + i += 1; + keep + }); + // data[0..first_removed] is untouched, so we only need to rebuild the tail: + self.rebuild_tail(first_removed); + } +} + +impl<T> BinaryHeap<T> { + /// Returns an iterator visiting all values in the underlying vector, in + /// arbitrary order. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let heap = BinaryHeap::from([1, 2, 3, 4]); + /// + /// // Print 1, 2, 3, 4 in arbitrary order + /// for x in heap.iter() { + /// println!("{x}"); + /// } + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn iter(&self) -> Iter<'_, T> { + Iter { iter: self.data.iter() } + } + + /// Returns an iterator which retrieves elements in heap order. + /// This method consumes the original heap. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// #![feature(binary_heap_into_iter_sorted)] + /// use std::collections::BinaryHeap; + /// let heap = BinaryHeap::from([1, 2, 3, 4, 5]); + /// + /// assert_eq!(heap.into_iter_sorted().take(2).collect::<Vec<_>>(), [5, 4]); + /// ``` + #[unstable(feature = "binary_heap_into_iter_sorted", issue = "59278")] + pub fn into_iter_sorted(self) -> IntoIterSorted<T> { + IntoIterSorted { inner: self } + } + + /// Returns the greatest item in the binary heap, or `None` if it is empty. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let mut heap = BinaryHeap::new(); + /// assert_eq!(heap.peek(), None); + /// + /// heap.push(1); + /// heap.push(5); + /// heap.push(2); + /// assert_eq!(heap.peek(), Some(&5)); + /// + /// ``` + /// + /// # Time complexity + /// + /// Cost is *O*(1) in the worst case. + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn peek(&self) -> Option<&T> { + self.data.get(0) + } + + /// Returns the number of elements the binary heap can hold without reallocating. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let mut heap = BinaryHeap::with_capacity(100); + /// assert!(heap.capacity() >= 100); + /// heap.push(4); + /// ``` + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn capacity(&self) -> usize { + self.data.capacity() + } + + /// Reserves the minimum capacity for at least `additional` elements more than + /// the current length. Unlike [`reserve`], this will not + /// deliberately over-allocate to speculatively avoid frequent allocations. + /// After calling `reserve_exact`, capacity will be greater than or equal to + /// `self.len() + additional`. Does nothing if the capacity is already + /// sufficient. + /// + /// [`reserve`]: BinaryHeap::reserve + /// + /// # Panics + /// + /// Panics if the new capacity overflows [`usize`]. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let mut heap = BinaryHeap::new(); + /// heap.reserve_exact(100); + /// assert!(heap.capacity() >= 100); + /// heap.push(4); + /// ``` + /// + /// [`reserve`]: BinaryHeap::reserve + #[stable(feature = "rust1", since = "1.0.0")] + pub fn reserve_exact(&mut self, additional: usize) { + self.data.reserve_exact(additional); + } + + /// Reserves capacity for at least `additional` elements more than the + /// current length. The allocator may reserve more space to speculatively + /// avoid frequent allocations. After calling `reserve`, + /// capacity will be greater than or equal to `self.len() + additional`. + /// Does nothing if capacity is already sufficient. + /// + /// # Panics + /// + /// Panics if the new capacity overflows [`usize`]. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let mut heap = BinaryHeap::new(); + /// heap.reserve(100); + /// assert!(heap.capacity() >= 100); + /// heap.push(4); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn reserve(&mut self, additional: usize) { + self.data.reserve(additional); + } + + /// Tries to reserve the minimum capacity for at least `additional` elements + /// more than the current length. Unlike [`try_reserve`], this will not + /// deliberately over-allocate to speculatively avoid frequent allocations. + /// After calling `try_reserve_exact`, capacity will be greater than or + /// equal to `self.len() + additional` if it returns `Ok(())`. + /// Does nothing if the capacity is already sufficient. + /// + /// Note that the allocator may give the collection more space than it + /// requests. Therefore, capacity can not be relied upon to be precisely + /// minimal. Prefer [`try_reserve`] if future insertions are expected. + /// + /// [`try_reserve`]: BinaryHeap::try_reserve + /// + /// # Errors + /// + /// If the capacity overflows, or the allocator reports a failure, then an error + /// is returned. + /// + /// # Examples + /// + /// ``` + /// use std::collections::BinaryHeap; + /// use std::collections::TryReserveError; + /// + /// fn find_max_slow(data: &[u32]) -> Result<Option<u32>, TryReserveError> { + /// let mut heap = BinaryHeap::new(); + /// + /// // Pre-reserve the memory, exiting if we can't + /// heap.try_reserve_exact(data.len())?; + /// + /// // Now we know this can't OOM in the middle of our complex work + /// heap.extend(data.iter()); + /// + /// Ok(heap.pop()) + /// } + /// # find_max_slow(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?"); + /// ``` + #[stable(feature = "try_reserve_2", since = "1.63.0")] + pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), TryReserveError> { + self.data.try_reserve_exact(additional) + } + + /// Tries to reserve capacity for at least `additional` elements more than the + /// current length. The allocator may reserve more space to speculatively + /// avoid frequent allocations. After calling `try_reserve`, capacity will be + /// greater than or equal to `self.len() + additional` if it returns + /// `Ok(())`. Does nothing if capacity is already sufficient. This method + /// preserves the contents even if an error occurs. + /// + /// # Errors + /// + /// If the capacity overflows, or the allocator reports a failure, then an error + /// is returned. + /// + /// # Examples + /// + /// ``` + /// use std::collections::BinaryHeap; + /// use std::collections::TryReserveError; + /// + /// fn find_max_slow(data: &[u32]) -> Result<Option<u32>, TryReserveError> { + /// let mut heap = BinaryHeap::new(); + /// + /// // Pre-reserve the memory, exiting if we can't + /// heap.try_reserve(data.len())?; + /// + /// // Now we know this can't OOM in the middle of our complex work + /// heap.extend(data.iter()); + /// + /// Ok(heap.pop()) + /// } + /// # find_max_slow(&[1, 2, 3]).expect("why is the test harness OOMing on 12 bytes?"); + /// ``` + #[stable(feature = "try_reserve_2", since = "1.63.0")] + pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> { + self.data.try_reserve(additional) + } + + /// Discards as much additional capacity as possible. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let mut heap: BinaryHeap<i32> = BinaryHeap::with_capacity(100); + /// + /// assert!(heap.capacity() >= 100); + /// heap.shrink_to_fit(); + /// assert!(heap.capacity() == 0); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn shrink_to_fit(&mut self) { + self.data.shrink_to_fit(); + } + + /// Discards capacity with a lower bound. + /// + /// The capacity will remain at least as large as both the length + /// and the supplied value. + /// + /// If the current capacity is less than the lower limit, this is a no-op. + /// + /// # Examples + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let mut heap: BinaryHeap<i32> = BinaryHeap::with_capacity(100); + /// + /// assert!(heap.capacity() >= 100); + /// heap.shrink_to(10); + /// assert!(heap.capacity() >= 10); + /// ``` + #[inline] + #[stable(feature = "shrink_to", since = "1.56.0")] + pub fn shrink_to(&mut self, min_capacity: usize) { + self.data.shrink_to(min_capacity) + } + + /// Returns a slice of all values in the underlying vector, in arbitrary + /// order. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// #![feature(binary_heap_as_slice)] + /// use std::collections::BinaryHeap; + /// use std::io::{self, Write}; + /// + /// let heap = BinaryHeap::from([1, 2, 3, 4, 5, 6, 7]); + /// + /// io::sink().write(heap.as_slice()).unwrap(); + /// ``` + #[must_use] + #[unstable(feature = "binary_heap_as_slice", issue = "83659")] + pub fn as_slice(&self) -> &[T] { + self.data.as_slice() + } + + /// Consumes the `BinaryHeap` and returns the underlying vector + /// in arbitrary order. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let heap = BinaryHeap::from([1, 2, 3, 4, 5, 6, 7]); + /// let vec = heap.into_vec(); + /// + /// // Will print in some order + /// for x in vec { + /// println!("{x}"); + /// } + /// ``` + #[must_use = "`self` will be dropped if the result is not used"] + #[stable(feature = "binary_heap_extras_15", since = "1.5.0")] + pub fn into_vec(self) -> Vec<T> { + self.into() + } + + /// Returns the length of the binary heap. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let heap = BinaryHeap::from([1, 3]); + /// + /// assert_eq!(heap.len(), 2); + /// ``` + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn len(&self) -> usize { + self.data.len() + } + + /// Checks if the binary heap is empty. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let mut heap = BinaryHeap::new(); + /// + /// assert!(heap.is_empty()); + /// + /// heap.push(3); + /// heap.push(5); + /// heap.push(1); + /// + /// assert!(!heap.is_empty()); + /// ``` + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn is_empty(&self) -> bool { + self.len() == 0 + } + + /// Clears the binary heap, returning an iterator over the removed elements + /// in arbitrary order. If the iterator is dropped before being fully + /// consumed, it drops the remaining elements in arbitrary order. + /// + /// The returned iterator keeps a mutable borrow on the heap to optimize + /// its implementation. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let mut heap = BinaryHeap::from([1, 3]); + /// + /// assert!(!heap.is_empty()); + /// + /// for x in heap.drain() { + /// println!("{x}"); + /// } + /// + /// assert!(heap.is_empty()); + /// ``` + #[inline] + #[stable(feature = "drain", since = "1.6.0")] + pub fn drain(&mut self) -> Drain<'_, T> { + Drain { iter: self.data.drain(..) } + } + + /// Drops all items from the binary heap. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let mut heap = BinaryHeap::from([1, 3]); + /// + /// assert!(!heap.is_empty()); + /// + /// heap.clear(); + /// + /// assert!(heap.is_empty()); + /// ``` + #[stable(feature = "rust1", since = "1.0.0")] + pub fn clear(&mut self) { + self.drain(); + } +} + +/// Hole represents a hole in a slice i.e., an index without valid value +/// (because it was moved from or duplicated). +/// In drop, `Hole` will restore the slice by filling the hole +/// position with the value that was originally removed. +struct Hole<'a, T: 'a> { + data: &'a mut [T], + elt: ManuallyDrop<T>, + pos: usize, +} + +impl<'a, T> Hole<'a, T> { + /// Create a new `Hole` at index `pos`. + /// + /// Unsafe because pos must be within the data slice. + #[inline] + unsafe fn new(data: &'a mut [T], pos: usize) -> Self { + debug_assert!(pos < data.len()); + // SAFE: pos should be inside the slice + let elt = unsafe { ptr::read(data.get_unchecked(pos)) }; + Hole { data, elt: ManuallyDrop::new(elt), pos } + } + + #[inline] + fn pos(&self) -> usize { + self.pos + } + + /// Returns a reference to the element removed. + #[inline] + fn element(&self) -> &T { + &self.elt + } + + /// Returns a reference to the element at `index`. + /// + /// Unsafe because index must be within the data slice and not equal to pos. + #[inline] + unsafe fn get(&self, index: usize) -> &T { + debug_assert!(index != self.pos); + debug_assert!(index < self.data.len()); + unsafe { self.data.get_unchecked(index) } + } + + /// Move hole to new location + /// + /// Unsafe because index must be within the data slice and not equal to pos. + #[inline] + unsafe fn move_to(&mut self, index: usize) { + debug_assert!(index != self.pos); + debug_assert!(index < self.data.len()); + unsafe { + let ptr = self.data.as_mut_ptr(); + let index_ptr: *const _ = ptr.add(index); + let hole_ptr = ptr.add(self.pos); + ptr::copy_nonoverlapping(index_ptr, hole_ptr, 1); + } + self.pos = index; + } +} + +impl<T> Drop for Hole<'_, T> { + #[inline] + fn drop(&mut self) { + // fill the hole again + unsafe { + let pos = self.pos; + ptr::copy_nonoverlapping(&*self.elt, self.data.get_unchecked_mut(pos), 1); + } + } +} + +/// An iterator over the elements of a `BinaryHeap`. +/// +/// This `struct` is created by [`BinaryHeap::iter()`]. See its +/// documentation for more. +/// +/// [`iter`]: BinaryHeap::iter +#[must_use = "iterators are lazy and do nothing unless consumed"] +#[stable(feature = "rust1", since = "1.0.0")] +pub struct Iter<'a, T: 'a> { + iter: slice::Iter<'a, T>, +} + +#[stable(feature = "collection_debug", since = "1.17.0")] +impl<T: fmt::Debug> fmt::Debug for Iter<'_, T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_tuple("Iter").field(&self.iter.as_slice()).finish() + } +} + +// FIXME(#26925) Remove in favor of `#[derive(Clone)]` +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> Clone for Iter<'_, T> { + fn clone(&self) -> Self { + Iter { iter: self.iter.clone() } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, T> Iterator for Iter<'a, T> { + type Item = &'a T; + + #[inline] + fn next(&mut self) -> Option<&'a T> { + self.iter.next() + } + + #[inline] + fn size_hint(&self) -> (usize, Option<usize>) { + self.iter.size_hint() + } + + #[inline] + fn last(self) -> Option<&'a T> { + self.iter.last() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, T> DoubleEndedIterator for Iter<'a, T> { + #[inline] + fn next_back(&mut self) -> Option<&'a T> { + self.iter.next_back() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> ExactSizeIterator for Iter<'_, T> { + fn is_empty(&self) -> bool { + self.iter.is_empty() + } +} + +#[stable(feature = "fused", since = "1.26.0")] +impl<T> FusedIterator for Iter<'_, T> {} + +/// An owning iterator over the elements of a `BinaryHeap`. +/// +/// This `struct` is created by [`BinaryHeap::into_iter()`] +/// (provided by the [`IntoIterator`] trait). See its documentation for more. +/// +/// [`into_iter`]: BinaryHeap::into_iter +/// [`IntoIterator`]: core::iter::IntoIterator +#[stable(feature = "rust1", since = "1.0.0")] +#[derive(Clone)] +pub struct IntoIter<T> { + iter: vec::IntoIter<T>, +} + +#[stable(feature = "collection_debug", since = "1.17.0")] +impl<T: fmt::Debug> fmt::Debug for IntoIter<T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_tuple("IntoIter").field(&self.iter.as_slice()).finish() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> Iterator for IntoIter<T> { + type Item = T; + + #[inline] + fn next(&mut self) -> Option<T> { + self.iter.next() + } + + #[inline] + fn size_hint(&self) -> (usize, Option<usize>) { + self.iter.size_hint() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> DoubleEndedIterator for IntoIter<T> { + #[inline] + fn next_back(&mut self) -> Option<T> { + self.iter.next_back() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> ExactSizeIterator for IntoIter<T> { + fn is_empty(&self) -> bool { + self.iter.is_empty() + } +} + +#[stable(feature = "fused", since = "1.26.0")] +impl<T> FusedIterator for IntoIter<T> {} + +// In addition to the SAFETY invariants of the following three unsafe traits +// also refer to the vec::in_place_collect module documentation to get an overview +#[unstable(issue = "none", feature = "inplace_iteration")] +#[doc(hidden)] +unsafe impl<T> SourceIter for IntoIter<T> { + type Source = IntoIter<T>; + + #[inline] + unsafe fn as_inner(&mut self) -> &mut Self::Source { + self + } +} + +#[unstable(issue = "none", feature = "inplace_iteration")] +#[doc(hidden)] +unsafe impl<I> InPlaceIterable for IntoIter<I> {} + +unsafe impl<I> AsVecIntoIter for IntoIter<I> { + type Item = I; + + fn as_into_iter(&mut self) -> &mut vec::IntoIter<Self::Item> { + &mut self.iter + } +} + +#[must_use = "iterators are lazy and do nothing unless consumed"] +#[unstable(feature = "binary_heap_into_iter_sorted", issue = "59278")] +#[derive(Clone, Debug)] +pub struct IntoIterSorted<T> { + inner: BinaryHeap<T>, +} + +#[unstable(feature = "binary_heap_into_iter_sorted", issue = "59278")] +impl<T: Ord> Iterator for IntoIterSorted<T> { + type Item = T; + + #[inline] + fn next(&mut self) -> Option<T> { + self.inner.pop() + } + + #[inline] + fn size_hint(&self) -> (usize, Option<usize>) { + let exact = self.inner.len(); + (exact, Some(exact)) + } +} + +#[unstable(feature = "binary_heap_into_iter_sorted", issue = "59278")] +impl<T: Ord> ExactSizeIterator for IntoIterSorted<T> {} + +#[unstable(feature = "binary_heap_into_iter_sorted", issue = "59278")] +impl<T: Ord> FusedIterator for IntoIterSorted<T> {} + +#[unstable(feature = "trusted_len", issue = "37572")] +unsafe impl<T: Ord> TrustedLen for IntoIterSorted<T> {} + +/// A draining iterator over the elements of a `BinaryHeap`. +/// +/// This `struct` is created by [`BinaryHeap::drain()`]. See its +/// documentation for more. +/// +/// [`drain`]: BinaryHeap::drain +#[stable(feature = "drain", since = "1.6.0")] +#[derive(Debug)] +pub struct Drain<'a, T: 'a> { + iter: vec::Drain<'a, T>, +} + +#[stable(feature = "drain", since = "1.6.0")] +impl<T> Iterator for Drain<'_, T> { + type Item = T; + + #[inline] + fn next(&mut self) -> Option<T> { + self.iter.next() + } + + #[inline] + fn size_hint(&self) -> (usize, Option<usize>) { + self.iter.size_hint() + } +} + +#[stable(feature = "drain", since = "1.6.0")] +impl<T> DoubleEndedIterator for Drain<'_, T> { + #[inline] + fn next_back(&mut self) -> Option<T> { + self.iter.next_back() + } +} + +#[stable(feature = "drain", since = "1.6.0")] +impl<T> ExactSizeIterator for Drain<'_, T> { + fn is_empty(&self) -> bool { + self.iter.is_empty() + } +} + +#[stable(feature = "fused", since = "1.26.0")] +impl<T> FusedIterator for Drain<'_, T> {} + +/// A draining iterator over the elements of a `BinaryHeap`. +/// +/// This `struct` is created by [`BinaryHeap::drain_sorted()`]. See its +/// documentation for more. +/// +/// [`drain_sorted`]: BinaryHeap::drain_sorted +#[unstable(feature = "binary_heap_drain_sorted", issue = "59278")] +#[derive(Debug)] +pub struct DrainSorted<'a, T: Ord> { + inner: &'a mut BinaryHeap<T>, +} + +#[unstable(feature = "binary_heap_drain_sorted", issue = "59278")] +impl<'a, T: Ord> Drop for DrainSorted<'a, T> { + /// Removes heap elements in heap order. + fn drop(&mut self) { + struct DropGuard<'r, 'a, T: Ord>(&'r mut DrainSorted<'a, T>); + + impl<'r, 'a, T: Ord> Drop for DropGuard<'r, 'a, T> { + fn drop(&mut self) { + while self.0.inner.pop().is_some() {} + } + } + + while let Some(item) = self.inner.pop() { + let guard = DropGuard(self); + drop(item); + mem::forget(guard); + } + } +} + +#[unstable(feature = "binary_heap_drain_sorted", issue = "59278")] +impl<T: Ord> Iterator for DrainSorted<'_, T> { + type Item = T; + + #[inline] + fn next(&mut self) -> Option<T> { + self.inner.pop() + } + + #[inline] + fn size_hint(&self) -> (usize, Option<usize>) { + let exact = self.inner.len(); + (exact, Some(exact)) + } +} + +#[unstable(feature = "binary_heap_drain_sorted", issue = "59278")] +impl<T: Ord> ExactSizeIterator for DrainSorted<'_, T> {} + +#[unstable(feature = "binary_heap_drain_sorted", issue = "59278")] +impl<T: Ord> FusedIterator for DrainSorted<'_, T> {} + +#[unstable(feature = "trusted_len", issue = "37572")] +unsafe impl<T: Ord> TrustedLen for DrainSorted<'_, T> {} + +#[stable(feature = "binary_heap_extras_15", since = "1.5.0")] +impl<T: Ord> From<Vec<T>> for BinaryHeap<T> { + /// Converts a `Vec<T>` into a `BinaryHeap<T>`. + /// + /// This conversion happens in-place, and has *O*(*n*) time complexity. + fn from(vec: Vec<T>) -> BinaryHeap<T> { + let mut heap = BinaryHeap { data: vec }; + heap.rebuild(); + heap + } +} + +#[stable(feature = "std_collections_from_array", since = "1.56.0")] +impl<T: Ord, const N: usize> From<[T; N]> for BinaryHeap<T> { + /// ``` + /// use std::collections::BinaryHeap; + /// + /// let mut h1 = BinaryHeap::from([1, 4, 2, 3]); + /// let mut h2: BinaryHeap<_> = [1, 4, 2, 3].into(); + /// while let Some((a, b)) = h1.pop().zip(h2.pop()) { + /// assert_eq!(a, b); + /// } + /// ``` + fn from(arr: [T; N]) -> Self { + Self::from_iter(arr) + } +} + +#[stable(feature = "binary_heap_extras_15", since = "1.5.0")] +impl<T> From<BinaryHeap<T>> for Vec<T> { + /// Converts a `BinaryHeap<T>` into a `Vec<T>`. + /// + /// This conversion requires no data movement or allocation, and has + /// constant time complexity. + fn from(heap: BinaryHeap<T>) -> Vec<T> { + heap.data + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Ord> FromIterator<T> for BinaryHeap<T> { + fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> BinaryHeap<T> { + BinaryHeap::from(iter.into_iter().collect::<Vec<_>>()) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T> IntoIterator for BinaryHeap<T> { + type Item = T; + type IntoIter = IntoIter<T>; + + /// Creates a consuming iterator, that is, one that moves each value out of + /// the binary heap in arbitrary order. The binary heap cannot be used + /// after calling this. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// use std::collections::BinaryHeap; + /// let heap = BinaryHeap::from([1, 2, 3, 4]); + /// + /// // Print 1, 2, 3, 4 in arbitrary order + /// for x in heap.into_iter() { + /// // x has type i32, not &i32 + /// println!("{x}"); + /// } + /// ``` + fn into_iter(self) -> IntoIter<T> { + IntoIter { iter: self.data.into_iter() } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<'a, T> IntoIterator for &'a BinaryHeap<T> { + type Item = &'a T; + type IntoIter = Iter<'a, T>; + + fn into_iter(self) -> Iter<'a, T> { + self.iter() + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<T: Ord> Extend<T> for BinaryHeap<T> { + #[inline] + fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) { + <Self as SpecExtend<I>>::spec_extend(self, iter); + } + + #[inline] + fn extend_one(&mut self, item: T) { + self.push(item); + } + + #[inline] + fn extend_reserve(&mut self, additional: usize) { + self.reserve(additional); + } +} + +impl<T: Ord, I: IntoIterator<Item = T>> SpecExtend<I> for BinaryHeap<T> { + default fn spec_extend(&mut self, iter: I) { + self.extend_desugared(iter.into_iter()); + } +} + +impl<T: Ord> SpecExtend<Vec<T>> for BinaryHeap<T> { + fn spec_extend(&mut self, ref mut other: Vec<T>) { + let start = self.data.len(); + self.data.append(other); + self.rebuild_tail(start); + } +} + +impl<T: Ord> SpecExtend<BinaryHeap<T>> for BinaryHeap<T> { + fn spec_extend(&mut self, ref mut other: BinaryHeap<T>) { + self.append(other); + } +} + +impl<T: Ord> BinaryHeap<T> { + fn extend_desugared<I: IntoIterator<Item = T>>(&mut self, iter: I) { + let iterator = iter.into_iter(); + let (lower, _) = iterator.size_hint(); + + self.reserve(lower); + + iterator.for_each(move |elem| self.push(elem)); + } +} + +#[stable(feature = "extend_ref", since = "1.2.0")] +impl<'a, T: 'a + Ord + Copy> Extend<&'a T> for BinaryHeap<T> { + fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) { + self.extend(iter.into_iter().cloned()); + } + + #[inline] + fn extend_one(&mut self, &item: &'a T) { + self.push(item); + } + + #[inline] + fn extend_reserve(&mut self, additional: usize) { + self.reserve(additional); + } +} |