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// Copyright 2009 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.
// The list package implements a doubly linked list.
//
// To iterate over a list (where l is a *List):
// for e := l.Front(); e != nil; e = e.Next() {
// // do something with e.Value
// }
//
package list
// Element is an element in the linked list.
type Element struct {
// Next and previous pointers in the doubly-linked list of elements.
// The front of the list has prev = nil, and the back has next = nil.
next, prev *Element
// The list to which this element belongs.
list *List
// The contents of this list element.
Value interface{}
}
// Next returns the next list element or nil.
func (e *Element) Next() *Element { return e.next }
// Prev returns the previous list element or nil.
func (e *Element) Prev() *Element { return e.prev }
// List represents a doubly linked list.
// The zero value for List is an empty list ready to use.
type List struct {
front, back *Element
len int
}
// Init initializes or clears a List.
func (l *List) Init() *List {
l.front = nil
l.back = nil
l.len = 0
return l
}
// New returns an initialized list.
func New() *List { return new(List) }
// Front returns the first element in the list.
func (l *List) Front() *Element { return l.front }
// Back returns the last element in the list.
func (l *List) Back() *Element { return l.back }
// Remove removes the element from the list
// and returns its Value.
func (l *List) Remove(e *Element) interface{} {
l.remove(e)
e.list = nil // do what remove does not
return e.Value
}
// remove the element from the list, but do not clear the Element's list field.
// This is so that other List methods may use remove when relocating Elements
// without needing to restore the list field.
func (l *List) remove(e *Element) {
if e.list != l {
return
}
if e.prev == nil {
l.front = e.next
} else {
e.prev.next = e.next
}
if e.next == nil {
l.back = e.prev
} else {
e.next.prev = e.prev
}
e.prev = nil
e.next = nil
l.len--
}
func (l *List) insertBefore(e *Element, mark *Element) {
if mark.prev == nil {
// new front of the list
l.front = e
} else {
mark.prev.next = e
}
e.prev = mark.prev
mark.prev = e
e.next = mark
l.len++
}
func (l *List) insertAfter(e *Element, mark *Element) {
if mark.next == nil {
// new back of the list
l.back = e
} else {
mark.next.prev = e
}
e.next = mark.next
mark.next = e
e.prev = mark
l.len++
}
func (l *List) insertFront(e *Element) {
if l.front == nil {
// empty list
l.front, l.back = e, e
e.prev, e.next = nil, nil
l.len = 1
return
}
l.insertBefore(e, l.front)
}
func (l *List) insertBack(e *Element) {
if l.back == nil {
// empty list
l.front, l.back = e, e
e.prev, e.next = nil, nil
l.len = 1
return
}
l.insertAfter(e, l.back)
}
// PushFront inserts the value at the front of the list and returns a new Element containing the value.
func (l *List) PushFront(value interface{}) *Element {
e := &Element{nil, nil, l, value}
l.insertFront(e)
return e
}
// PushBack inserts the value at the back of the list and returns a new Element containing the value.
func (l *List) PushBack(value interface{}) *Element {
e := &Element{nil, nil, l, value}
l.insertBack(e)
return e
}
// InsertBefore inserts the value immediately before mark and returns a new Element containing the value.
func (l *List) InsertBefore(value interface{}, mark *Element) *Element {
if mark.list != l {
return nil
}
e := &Element{nil, nil, l, value}
l.insertBefore(e, mark)
return e
}
// InsertAfter inserts the value immediately after mark and returns a new Element containing the value.
func (l *List) InsertAfter(value interface{}, mark *Element) *Element {
if mark.list != l {
return nil
}
e := &Element{nil, nil, l, value}
l.insertAfter(e, mark)
return e
}
// MoveToFront moves the element to the front of the list.
func (l *List) MoveToFront(e *Element) {
if e.list != l || l.front == e {
return
}
l.remove(e)
l.insertFront(e)
}
// MoveToBack moves the element to the back of the list.
func (l *List) MoveToBack(e *Element) {
if e.list != l || l.back == e {
return
}
l.remove(e)
l.insertBack(e)
}
// Len returns the number of elements in the list.
func (l *List) Len() int { return l.len }
// PushBackList inserts each element of ol at the back of the list.
func (l *List) PushBackList(ol *List) {
last := ol.Back()
for e := ol.Front(); e != nil; e = e.Next() {
l.PushBack(e.Value)
if e == last {
break
}
}
}
// PushFrontList inserts each element of ol at the front of the list. The ordering of the passed list is preserved.
func (l *List) PushFrontList(ol *List) {
first := ol.Front()
for e := ol.Back(); e != nil; e = e.Prev() {
l.PushFront(e.Value)
if e == first {
break
}
}
}
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