| // 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 a |
| |
| import ( |
| "fmt" |
| ) |
| |
| // 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)) |
| } |
| } |
| } |