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// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// The list package implements a doubly linked list.
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// To iterate over a list (where l is a *List):
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// for e := l.Front(); e != nil; e = e.Next() {
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// // do something with e.Value
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// Element is an element in the linked list.
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// Next and previous pointers in the doubly-linked list of elements.
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// The front of the list has prev = nil, and the back has next = nil.
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// The list to which this element belongs.
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// The contents of this list element.
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// Next returns the next list element or nil.
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func (e *Element) Next() *Element { return e.next }
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// Prev returns the previous list element or nil.
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func (e *Element) Prev() *Element { return e.prev }
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// List represents a doubly linked list.
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// The zero value for List is an empty list ready to use.
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// Init initializes or clears a List.
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func (l *List) Init() *List {
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// New returns an initialized list.
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func New() *List { return new(List) }
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// Front returns the first element in the list.
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func (l *List) Front() *Element { return l.front }
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// Back returns the last element in the list.
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func (l *List) Back() *Element { return l.back }
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// Remove removes the element from the list
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// and returns its Value.
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func (l *List) Remove(e *Element) interface{} {
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e.list = nil // do what remove does not
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// remove the element from the list, but do not clear the Element's list field.
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// This is so that other List methods may use remove when relocating Elements
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// without needing to restore the list field.
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func (l *List) remove(e *Element) {
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func (l *List) insertBefore(e *Element, mark *Element) {
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// new front of the list
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func (l *List) insertAfter(e *Element, mark *Element) {
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if mark.next == nil {
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// new back of the list
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func (l *List) insertFront(e *Element) {
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l.front, l.back = e, e
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e.prev, e.next = nil, nil
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l.insertBefore(e, l.front)
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func (l *List) insertBack(e *Element) {
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l.front, l.back = e, e
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e.prev, e.next = nil, nil
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l.insertAfter(e, l.back)
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// PushFront inserts the value at the front of the list and returns a new Element containing the value.
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func (l *List) PushFront(value interface{}) *Element {
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e := &Element{nil, nil, l, value}
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// PushBack inserts the value at the back of the list and returns a new Element containing the value.
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func (l *List) PushBack(value interface{}) *Element {
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e := &Element{nil, nil, l, value}
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// InsertBefore inserts the value immediately before mark and returns a new Element containing the value.
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func (l *List) InsertBefore(value interface{}, mark *Element) *Element {
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e := &Element{nil, nil, l, value}
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l.insertBefore(e, mark)
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// InsertAfter inserts the value immediately after mark and returns a new Element containing the value.
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func (l *List) InsertAfter(value interface{}, mark *Element) *Element {
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e := &Element{nil, nil, l, value}
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l.insertAfter(e, mark)
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// MoveToFront moves the element to the front of the list.
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func (l *List) MoveToFront(e *Element) {
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if e.list != l || l.front == e {
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// MoveToBack moves the element to the back of the list.
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func (l *List) MoveToBack(e *Element) {
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if e.list != l || l.back == e {
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// Len returns the number of elements in the list.
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func (l *List) Len() int { return l.len }
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// PushBackList inserts each element of ol at the back of the list.
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func (l *List) PushBackList(ol *List) {
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for e := ol.Front(); e != nil; e = e.Next() {
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// PushFrontList inserts each element of ol at the front of the list. The ordering of the passed list is preserved.
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func (l *List) PushFrontList(ol *List) {
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for e := ol.Back(); e != nil; e = e.Prev() {