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|
// run
// Copyright 2021 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 list provides a doubly linked list of some element type
// (generic form of the "container/list" package).
package main
import (
"fmt"
"strconv"
)
// Element is an element of a linked list.
type _Element[T any] struct {
// Next and previous pointers in the doubly-linked list of elements.
// To simplify the implementation, internally a list l is implemented
// as a ring, such that &l.root is both the next element of the last
// list element (l.Back()) and the previous element of the first list
// element (l.Front()).
next, prev *_Element[T]
// The list to which this element belongs.
list *_List[T]
// The value stored with this element.
Value T
}
// Next returns the next list element or nil.
func (e *_Element[T]) Next() *_Element[T] {
if p := e.next; e.list != nil && p != &e.list.root {
return p
}
return nil
}
// Prev returns the previous list element or nil.
func (e *_Element[T]) Prev() *_Element[T] {
if p := e.prev; e.list != nil && p != &e.list.root {
return p
}
return nil
}
// _List represents a doubly linked list.
// The zero value for _List is an empty list ready to use.
type _List[T any] struct {
root _Element[T] // sentinel list element, only &root, root.prev, and root.next are used
len int // current list length excluding (this) sentinel element
}
// Init initializes or clears list l.
func (l *_List[T]) Init() *_List[T] {
l.root.next = &l.root
l.root.prev = &l.root
l.len = 0
return l
}
// New returns an initialized list.
func _New[T any]() *_List[T] { return new(_List[T]).Init() }
// Len returns the number of elements of list l.
// The complexity is O(1).
func (l *_List[_]) Len() int { return l.len }
// Front returns the first element of list l or nil if the list is empty.
func (l *_List[T]) Front() *_Element[T] {
if l.len == 0 {
return nil
}
return l.root.next
}
// Back returns the last element of list l or nil if the list is empty.
func (l *_List[T]) Back() *_Element[T] {
if l.len == 0 {
return nil
}
return l.root.prev
}
// lazyInit lazily initializes a zero _List value.
func (l *_List[_]) lazyInit() {
if l.root.next == nil {
l.Init()
}
}
// insert inserts e after at, increments l.len, and returns e.
func (l *_List[T]) insert(e, at *_Element[T]) *_Element[T] {
e.prev = at
e.next = at.next
e.prev.next = e
e.next.prev = e
e.list = l
l.len++
return e
}
// insertValue is a convenience wrapper for insert(&_Element[T]{Value: v}, at).
func (l *_List[T]) insertValue(v T, at *_Element[T]) *_Element[T] {
return l.insert(&_Element[T]{Value: v}, at)
}
// remove removes e from its list, decrements l.len, and returns e.
func (l *_List[T]) remove(e *_Element[T]) *_Element[T] {
e.prev.next = e.next
e.next.prev = e.prev
e.next = nil // avoid memory leaks
e.prev = nil // avoid memory leaks
e.list = nil
l.len--
return e
}
// move moves e to next to at and returns e.
func (l *_List[T]) move(e, at *_Element[T]) *_Element[T] {
if e == at {
return e
}
e.prev.next = e.next
e.next.prev = e.prev
e.prev = at
e.next = at.next
e.prev.next = e
e.next.prev = e
return e
}
// Remove removes e from l if e is an element of list l.
// It returns the element value e.Value.
// The element must not be nil.
func (l *_List[T]) Remove(e *_Element[T]) T {
if e.list == l {
// if e.list == l, l must have been initialized when e was inserted
// in l or l == nil (e is a zero _Element) and l.remove will crash
l.remove(e)
}
return e.Value
}
// PushFront inserts a new element e with value v at the front of list l and returns e.
func (l *_List[T]) PushFront(v T) *_Element[T] {
l.lazyInit()
return l.insertValue(v, &l.root)
}
// PushBack inserts a new element e with value v at the back of list l and returns e.
func (l *_List[T]) PushBack(v T) *_Element[T] {
l.lazyInit()
return l.insertValue(v, l.root.prev)
}
// InsertBefore inserts a new element e with value v immediately before mark and returns e.
// If mark is not an element of l, the list is not modified.
// The mark must not be nil.
func (l *_List[T]) InsertBefore(v T, mark *_Element[T]) *_Element[T] {
if mark.list != l {
return nil
}
// see comment in _List.Remove about initialization of l
return l.insertValue(v, mark.prev)
}
// InsertAfter inserts a new element e with value v immediately after mark and returns e.
// If mark is not an element of l, the list is not modified.
// The mark must not be nil.
func (l *_List[T]) InsertAfter(v T, mark *_Element[T]) *_Element[T] {
if mark.list != l {
return nil
}
// see comment in _List.Remove about initialization of l
return l.insertValue(v, mark)
}
// MoveToFront moves element e to the front of list l.
// If e is not an element of l, the list is not modified.
// The element must not be nil.
func (l *_List[T]) MoveToFront(e *_Element[T]) {
if e.list != l || l.root.next == e {
return
}
// see comment in _List.Remove about initialization of l
l.move(e, &l.root)
}
// MoveToBack moves element e to the back of list l.
// If e is not an element of l, the list is not modified.
// The element must not be nil.
func (l *_List[T]) MoveToBack(e *_Element[T]) {
if e.list != l || l.root.prev == e {
return
}
// see comment in _List.Remove about initialization of l
l.move(e, l.root.prev)
}
// MoveBefore moves element e to its new position before mark.
// If e or mark is not an element of l, or e == mark, the list is not modified.
// The element and mark must not be nil.
func (l *_List[T]) MoveBefore(e, mark *_Element[T]) {
if e.list != l || e == mark || mark.list != l {
return
}
l.move(e, mark.prev)
}
// MoveAfter moves element e to its new position after mark.
// If e or mark is not an element of l, or e == mark, the list is not modified.
// The element and mark must not be nil.
func (l *_List[T]) MoveAfter(e, mark *_Element[T]) {
if e.list != l || e == mark || mark.list != l {
return
}
l.move(e, mark)
}
// PushBackList inserts a copy of an other list at the back of list l.
// The lists l and other may be the same. They must not be nil.
func (l *_List[T]) PushBackList(other *_List[T]) {
l.lazyInit()
for i, e := other.Len(), other.Front(); i > 0; i, e = i-1, e.Next() {
l.insertValue(e.Value, l.root.prev)
}
}
// PushFrontList inserts a copy of an other list at the front of list l.
// The lists l and other may be the same. They must not be nil.
func (l *_List[T]) PushFrontList(other *_List[T]) {
l.lazyInit()
for i, e := other.Len(), other.Back(); i > 0; i, e = i-1, e.Prev() {
l.insertValue(e.Value, &l.root)
}
}
// Transform runs a transform function on a list returning a new list.
func _Transform[TElem1, TElem2 any](lst *_List[TElem1], f func(TElem1) TElem2) *_List[TElem2] {
ret := _New[TElem2]()
for p := lst.Front(); p != nil; p = p.Next() {
ret.PushBack(f(p.Value))
}
return ret
}
func checkListLen[T any](l *_List[T], len int) bool {
if n := l.Len(); n != len {
panic(fmt.Sprintf("l.Len() = %d, want %d", n, len))
return false
}
return true
}
func checkListPointers[T any](l *_List[T], es []*_Element[T]) {
root := &l.root
if !checkListLen(l, len(es)) {
return
}
// zero length lists must be the zero value or properly initialized (sentinel circle)
if len(es) == 0 {
if l.root.next != nil && l.root.next != root || l.root.prev != nil && l.root.prev != root {
panic(fmt.Sprintf("l.root.next = %p, l.root.prev = %p; both should both be nil or %p", l.root.next, l.root.prev, root))
}
return
}
// len(es) > 0
// check internal and external prev/next connections
for i, e := range es {
prev := root
Prev := (*_Element[T])(nil)
if i > 0 {
prev = es[i-1]
Prev = prev
}
if p := e.prev; p != prev {
panic(fmt.Sprintf("elt[%d](%p).prev = %p, want %p", i, e, p, prev))
}
if p := e.Prev(); p != Prev {
panic(fmt.Sprintf("elt[%d](%p).Prev() = %p, want %p", i, e, p, Prev))
}
next := root
Next := (*_Element[T])(nil)
if i < len(es)-1 {
next = es[i+1]
Next = next
}
if n := e.next; n != next {
panic(fmt.Sprintf("elt[%d](%p).next = %p, want %p", i, e, n, next))
}
if n := e.Next(); n != Next {
panic(fmt.Sprintf("elt[%d](%p).Next() = %p, want %p", i, e, n, Next))
}
}
}
func TestList() {
l := _New[string]()
checkListPointers(l, []*(_Element[string]){})
// Single element list
e := l.PushFront("a")
checkListPointers(l, []*(_Element[string]){e})
l.MoveToFront(e)
checkListPointers(l, []*(_Element[string]){e})
l.MoveToBack(e)
checkListPointers(l, []*(_Element[string]){e})
l.Remove(e)
checkListPointers(l, []*(_Element[string]){})
// Bigger list
l2 := _New[int]()
e2 := l2.PushFront(2)
e1 := l2.PushFront(1)
e3 := l2.PushBack(3)
e4 := l2.PushBack(600)
checkListPointers(l2, []*(_Element[int]){e1, e2, e3, e4})
l2.Remove(e2)
checkListPointers(l2, []*(_Element[int]){e1, e3, e4})
l2.MoveToFront(e3) // move from middle
checkListPointers(l2, []*(_Element[int]){e3, e1, e4})
l2.MoveToFront(e1)
l2.MoveToBack(e3) // move from middle
checkListPointers(l2, []*(_Element[int]){e1, e4, e3})
l2.MoveToFront(e3) // move from back
checkListPointers(l2, []*(_Element[int]){e3, e1, e4})
l2.MoveToFront(e3) // should be no-op
checkListPointers(l2, []*(_Element[int]){e3, e1, e4})
l2.MoveToBack(e3) // move from front
checkListPointers(l2, []*(_Element[int]){e1, e4, e3})
l2.MoveToBack(e3) // should be no-op
checkListPointers(l2, []*(_Element[int]){e1, e4, e3})
e2 = l2.InsertBefore(2, e1) // insert before front
checkListPointers(l2, []*(_Element[int]){e2, e1, e4, e3})
l2.Remove(e2)
e2 = l2.InsertBefore(2, e4) // insert before middle
checkListPointers(l2, []*(_Element[int]){e1, e2, e4, e3})
l2.Remove(e2)
e2 = l2.InsertBefore(2, e3) // insert before back
checkListPointers(l2, []*(_Element[int]){e1, e4, e2, e3})
l2.Remove(e2)
e2 = l2.InsertAfter(2, e1) // insert after front
checkListPointers(l2, []*(_Element[int]){e1, e2, e4, e3})
l2.Remove(e2)
e2 = l2.InsertAfter(2, e4) // insert after middle
checkListPointers(l2, []*(_Element[int]){e1, e4, e2, e3})
l2.Remove(e2)
e2 = l2.InsertAfter(2, e3) // insert after back
checkListPointers(l2, []*(_Element[int]){e1, e4, e3, e2})
l2.Remove(e2)
// Check standard iteration.
sum := 0
for e := l2.Front(); e != nil; e = e.Next() {
sum += e.Value
}
if sum != 604 {
panic(fmt.Sprintf("sum over l = %d, want 604", sum))
}
// Clear all elements by iterating
var next *_Element[int]
for e := l2.Front(); e != nil; e = next {
next = e.Next()
l2.Remove(e)
}
checkListPointers(l2, []*(_Element[int]){})
}
func checkList[T comparable](l *_List[T], es []interface{}) {
if !checkListLen(l, len(es)) {
return
}
i := 0
for e := l.Front(); e != nil; e = e.Next() {
le := e.Value
// Comparison between a generically-typed variable le and an interface.
if le != es[i] {
panic(fmt.Sprintf("elt[%d].Value = %v, want %v", i, le, es[i]))
}
i++
}
}
func TestExtending() {
l1 := _New[int]()
l2 := _New[int]()
l1.PushBack(1)
l1.PushBack(2)
l1.PushBack(3)
l2.PushBack(4)
l2.PushBack(5)
l3 := _New[int]()
l3.PushBackList(l1)
checkList(l3, []interface{}{1, 2, 3})
l3.PushBackList(l2)
checkList(l3, []interface{}{1, 2, 3, 4, 5})
l3 = _New[int]()
l3.PushFrontList(l2)
checkList(l3, []interface{}{4, 5})
l3.PushFrontList(l1)
checkList(l3, []interface{}{1, 2, 3, 4, 5})
checkList(l1, []interface{}{1, 2, 3})
checkList(l2, []interface{}{4, 5})
l3 = _New[int]()
l3.PushBackList(l1)
checkList(l3, []interface{}{1, 2, 3})
l3.PushBackList(l3)
checkList(l3, []interface{}{1, 2, 3, 1, 2, 3})
l3 = _New[int]()
l3.PushFrontList(l1)
checkList(l3, []interface{}{1, 2, 3})
l3.PushFrontList(l3)
checkList(l3, []interface{}{1, 2, 3, 1, 2, 3})
l3 = _New[int]()
l1.PushBackList(l3)
checkList(l1, []interface{}{1, 2, 3})
l1.PushFrontList(l3)
checkList(l1, []interface{}{1, 2, 3})
}
func TestRemove() {
l := _New[int]()
e1 := l.PushBack(1)
e2 := l.PushBack(2)
checkListPointers(l, []*(_Element[int]){e1, e2})
e := l.Front()
l.Remove(e)
checkListPointers(l, []*(_Element[int]){e2})
l.Remove(e)
checkListPointers(l, []*(_Element[int]){e2})
}
func TestIssue4103() {
l1 := _New[int]()
l1.PushBack(1)
l1.PushBack(2)
l2 := _New[int]()
l2.PushBack(3)
l2.PushBack(4)
e := l1.Front()
l2.Remove(e) // l2 should not change because e is not an element of l2
if n := l2.Len(); n != 2 {
panic(fmt.Sprintf("l2.Len() = %d, want 2", n))
}
l1.InsertBefore(8, e)
if n := l1.Len(); n != 3 {
panic(fmt.Sprintf("l1.Len() = %d, want 3", n))
}
}
func TestIssue6349() {
l := _New[int]()
l.PushBack(1)
l.PushBack(2)
e := l.Front()
l.Remove(e)
if e.Value != 1 {
panic(fmt.Sprintf("e.value = %d, want 1", e.Value))
}
if e.Next() != nil {
panic(fmt.Sprintf("e.Next() != nil"))
}
if e.Prev() != nil {
panic(fmt.Sprintf("e.Prev() != nil"))
}
}
func TestMove() {
l := _New[int]()
e1 := l.PushBack(1)
e2 := l.PushBack(2)
e3 := l.PushBack(3)
e4 := l.PushBack(4)
l.MoveAfter(e3, e3)
checkListPointers(l, []*(_Element[int]){e1, e2, e3, e4})
l.MoveBefore(e2, e2)
checkListPointers(l, []*(_Element[int]){e1, e2, e3, e4})
l.MoveAfter(e3, e2)
checkListPointers(l, []*(_Element[int]){e1, e2, e3, e4})
l.MoveBefore(e2, e3)
checkListPointers(l, []*(_Element[int]){e1, e2, e3, e4})
l.MoveBefore(e2, e4)
checkListPointers(l, []*(_Element[int]){e1, e3, e2, e4})
e2, e3 = e3, e2
l.MoveBefore(e4, e1)
checkListPointers(l, []*(_Element[int]){e4, e1, e2, e3})
e1, e2, e3, e4 = e4, e1, e2, e3
l.MoveAfter(e4, e1)
checkListPointers(l, []*(_Element[int]){e1, e4, e2, e3})
e2, e3, e4 = e4, e2, e3
l.MoveAfter(e2, e3)
checkListPointers(l, []*(_Element[int]){e1, e3, e2, e4})
e2, e3 = e3, e2
}
// Test PushFront, PushBack, PushFrontList, PushBackList with uninitialized _List
func TestZeroList() {
var l1 = new(_List[int])
l1.PushFront(1)
checkList(l1, []interface{}{1})
var l2 = new(_List[int])
l2.PushBack(1)
checkList(l2, []interface{}{1})
var l3 = new(_List[int])
l3.PushFrontList(l1)
checkList(l3, []interface{}{1})
var l4 = new(_List[int])
l4.PushBackList(l2)
checkList(l4, []interface{}{1})
}
// Test that a list l is not modified when calling InsertBefore with a mark that is not an element of l.
func TestInsertBeforeUnknownMark() {
var l _List[int]
l.PushBack(1)
l.PushBack(2)
l.PushBack(3)
l.InsertBefore(1, new(_Element[int]))
checkList(&l, []interface{}{1, 2, 3})
}
// Test that a list l is not modified when calling InsertAfter with a mark that is not an element of l.
func TestInsertAfterUnknownMark() {
var l _List[int]
l.PushBack(1)
l.PushBack(2)
l.PushBack(3)
l.InsertAfter(1, new(_Element[int]))
checkList(&l, []interface{}{1, 2, 3})
}
// Test that a list l is not modified when calling MoveAfter or MoveBefore with a mark that is not an element of l.
func TestMoveUnknownMark() {
var l1 _List[int]
e1 := l1.PushBack(1)
var l2 _List[int]
e2 := l2.PushBack(2)
l1.MoveAfter(e1, e2)
checkList(&l1, []interface{}{1})
checkList(&l2, []interface{}{2})
l1.MoveBefore(e1, e2)
checkList(&l1, []interface{}{1})
checkList(&l2, []interface{}{2})
}
// Test the Transform function.
func TestTransform() {
l1 := _New[int]()
l1.PushBack(1)
l1.PushBack(2)
l2 := _Transform(l1, strconv.Itoa)
checkList(l2, []interface{}{"1", "2"})
}
func main() {
TestList()
TestExtending()
TestRemove()
TestIssue4103()
TestIssue6349()
TestMove()
TestZeroList()
TestInsertBeforeUnknownMark()
TestInsertAfterUnknownMark()
TestTransform()
}
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