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// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package slices
import (
"math/bits"
"golang.org/x/exp/constraints"
)
// Sort sorts a slice of any ordered type in ascending order.
// Sort may fail to sort correctly when sorting slices of floating-point
// numbers containing Not-a-number (NaN) values.
// Use slices.SortFunc(x, func(a, b float64) bool {return a < b || (math.IsNaN(a) && !math.IsNaN(b))})
// instead if the input may contain NaNs.
func Sort[E constraints.Ordered](x []E) {
n := len(x)
pdqsortOrdered(x, 0, n, bits.Len(uint(n)))
}
// SortFunc sorts the slice x in ascending order as determined by the less function.
// This sort is not guaranteed to be stable.
//
// SortFunc requires that less is a strict weak ordering.
// See https://en.wikipedia.org/wiki/Weak_ordering#Strict_weak_orderings.
func SortFunc[E any](x []E, less func(a, b E) bool) {
n := len(x)
pdqsortLessFunc(x, 0, n, bits.Len(uint(n)), less)
}
// SortStable sorts the slice x while keeping the original order of equal
// elements, using less to compare elements.
func SortStableFunc[E any](x []E, less func(a, b E) bool) {
stableLessFunc(x, len(x), less)
}
// IsSorted reports whether x is sorted in ascending order.
func IsSorted[E constraints.Ordered](x []E) bool {
for i := len(x) - 1; i > 0; i-- {
if x[i] < x[i-1] {
return false
}
}
return true
}
// IsSortedFunc reports whether x is sorted in ascending order, with less as the
// comparison function.
func IsSortedFunc[E any](x []E, less func(a, b E) bool) bool {
for i := len(x) - 1; i > 0; i-- {
if less(x[i], x[i-1]) {
return false
}
}
return true
}
// BinarySearch searches for target in a sorted slice and returns the position
// where target is found, or the position where target would appear in the
// sort order; it also returns a bool saying whether the target is really found
// in the slice. The slice must be sorted in increasing order.
func BinarySearch[E constraints.Ordered](x []E, target E) (int, bool) {
// search returns the leftmost position where f returns true, or len(x) if f
// returns false for all x. This is the insertion position for target in x,
// and could point to an element that's either == target or not.
pos := search(len(x), func(i int) bool { return x[i] >= target })
if pos >= len(x) || x[pos] != target {
return pos, false
} else {
return pos, true
}
}
// BinarySearchFunc works like BinarySearch, but uses a custom comparison
// function. The slice must be sorted in increasing order, where "increasing" is
// defined by cmp. cmp(a, b) is expected to return an integer comparing the two
// parameters: 0 if a == b, a negative number if a < b and a positive number if
// a > b.
func BinarySearchFunc[E any](x []E, target E, cmp func(E, E) int) (int, bool) {
pos := search(len(x), func(i int) bool { return cmp(x[i], target) >= 0 })
if pos >= len(x) || cmp(x[pos], target) != 0 {
return pos, false
} else {
return pos, true
}
}
func search(n int, f func(int) bool) int {
// Define f(-1) == false and f(n) == true.
// Invariant: f(i-1) == false, f(j) == true.
i, j := 0, n
for i < j {
h := int(uint(i+j) >> 1) // avoid overflow when computing h
// i ≤ h < j
if !f(h) {
i = h + 1 // preserves f(i-1) == false
} else {
j = h // preserves f(j) == true
}
}
// i == j, f(i-1) == false, and f(j) (= f(i)) == true => answer is i.
return i
}
type sortedHint int // hint for pdqsort when choosing the pivot
const (
unknownHint sortedHint = iota
increasingHint
decreasingHint
)
// xorshift paper: https://www.jstatsoft.org/article/view/v008i14/xorshift.pdf
type xorshift uint64
func (r *xorshift) Next() uint64 {
*r ^= *r << 13
*r ^= *r >> 17
*r ^= *r << 5
return uint64(*r)
}
func nextPowerOfTwo(length int) uint {
return 1 << bits.Len(uint(length))
}
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