libgo/go/container/list/list.go

   1 // Copyright 2009 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // The list package implements a doubly linked list.
   6 //
   7 // To iterate over a list (where l is a *List):
   8 //      for e := l.Front(); e != nil; e = e.Next() {
   9 //              // do something with e.Value
  10 //      }
  11 //
  12 package list
  13
  14 // Element is an element in the linked list.
  15 type Element struct {
  16         // Next and previous pointers in the doubly-linked list of elements.
  17         // The front of the list has prev = nil, and the back has next = nil.
  18         next, prev *Element
  19
  20         // The list to which this element belongs.
  21         list *List
  22
  23         // The contents of this list element.
  24         Value interface{}
  25 }
  26
  27 // Next returns the next list element or nil.
  28 func (e *Element) Next() *Element { return e.next }
  29
  30 // Prev returns the previous list element or nil.
  31 func (e *Element) Prev() *Element { return e.prev }
  32
  33 // List represents a doubly linked list.
  34 // The zero value for List is an empty list ready to use.
  35 type List struct {
  36         front, back *Element
  37         len         int
  38 }
  39
  40 // Init initializes or clears a List.
  41 func (l *List) Init() *List {
  42         l.front = nil
  43         l.back = nil
  44         l.len = 0
  45         return l
  46 }
  47
  48 // New returns an initialized list.
  49 func New() *List { return new(List) }
  50
  51 // Front returns the first element in the list.
  52 func (l *List) Front() *Element { return l.front }
  53
  54 // Back returns the last element in the list.
  55 func (l *List) Back() *Element { return l.back }
  56
  57 // Remove removes the element from the list
  58 // and returns its Value.
  59 func (l *List) Remove(e *Element) interface{} {
  60         l.remove(e)
  61         e.list = nil // do what remove does not
  62         return e.Value
  63 }
  64
  65 // remove the element from the list, but do not clear the Element's list field.
  66 // This is so that other List methods may use remove when relocating Elements
  67 // without needing to restore the list field.
  68 func (l *List) remove(e *Element) {
  69         if e.list != l {
  70                 return
  71         }
  72         if e.prev == nil {
  73                 l.front = e.next
  74         } else {
  75                 e.prev.next = e.next
  76         }
  77         if e.next == nil {
  78                 l.back = e.prev
  79         } else {
  80                 e.next.prev = e.prev
  81         }
  82
  83         e.prev = nil
  84         e.next = nil
  85         l.len--
  86 }
  87
  88 func (l *List) insertBefore(e *Element, mark *Element) {
  89         if mark.prev == nil {
  90                 // new front of the list
  91                 l.front = e
  92         } else {
  93                 mark.prev.next = e
  94         }
  95         e.prev = mark.prev
  96         mark.prev = e
  97         e.next = mark
  98         l.len++
  99 }
 100
 101 func (l *List) insertAfter(e *Element, mark *Element) {
 102         if mark.next == nil {
 103                 // new back of the list
 104                 l.back = e
 105         } else {
 106                 mark.next.prev = e
 107         }
 108         e.next = mark.next
 109         mark.next = e
 110         e.prev = mark
 111         l.len++
 112 }
 113
 114 func (l *List) insertFront(e *Element) {
 115         if l.front == nil {
 116                 // empty list
 117                 l.front, l.back = e, e
 118                 e.prev, e.next = nil, nil
 119                 l.len = 1
 120                 return
 121         }
 122         l.insertBefore(e, l.front)
 123 }
 124
 125 func (l *List) insertBack(e *Element) {
 126         if l.back == nil {
 127                 // empty list
 128                 l.front, l.back = e, e
 129                 e.prev, e.next = nil, nil
 130                 l.len = 1
 131                 return
 132         }
 133         l.insertAfter(e, l.back)
 134 }
 135
 136 // PushFront inserts the value at the front of the list and returns a new Element containing the value.
 137 func (l *List) PushFront(value interface{}) *Element {
 138         e := &Element{nil, nil, l, value}
 139         l.insertFront(e)
 140         return e
 141 }
 142
 143 // PushBack inserts the value at the back of the list and returns a new Element containing the value.
 144 func (l *List) PushBack(value interface{}) *Element {
 145         e := &Element{nil, nil, l, value}
 146         l.insertBack(e)
 147         return e
 148 }
 149
 150 // InsertBefore inserts the value immediately before mark and returns a new Element containing the value.
 151 func (l *List) InsertBefore(value interface{}, mark *Element) *Element {
 152         if mark.list != l {
 153                 return nil
 154         }
 155         e := &Element{nil, nil, l, value}
 156         l.insertBefore(e, mark)
 157         return e
 158 }
 159
 160 // InsertAfter inserts the value immediately after mark and returns a new Element containing the value.
 161 func (l *List) InsertAfter(value interface{}, mark *Element) *Element {
 162         if mark.list != l {
 163                 return nil
 164         }
 165         e := &Element{nil, nil, l, value}
 166         l.insertAfter(e, mark)
 167         return e
 168 }
 169
 170 // MoveToFront moves the element to the front of the list.
 171 func (l *List) MoveToFront(e *Element) {
 172         if e.list != l || l.front == e {
 173                 return
 174         }
 175         l.remove(e)
 176         l.insertFront(e)
 177 }
 178
 179 // MoveToBack moves the element to the back of the list.
 180 func (l *List) MoveToBack(e *Element) {
 181         if e.list != l || l.back == e {
 182                 return
 183         }
 184         l.remove(e)
 185         l.insertBack(e)
 186 }
 187
 188 // Len returns the number of elements in the list.
 189 func (l *List) Len() int { return l.len }
 190
 191 // PushBackList inserts each element of ol at the back of the list.
 192 func (l *List) PushBackList(ol *List) {
 193         last := ol.Back()
 194         for e := ol.Front(); e != nil; e = e.Next() {
 195                 l.PushBack(e.Value)
 196                 if e == last {
 197                         break
 198                 }
 199         }
 200 }
 201
 202 // PushFrontList inserts each element of ol at the front of the list. The ordering of the passed list is preserved.
 203 func (l *List) PushFrontList(ol *List) {
 204         first := ol.Front()
 205         for e := ol.Back(); e != nil; e = e.Prev() {
 206                 l.PushFront(e.Value)
 207                 if e == first {
 208                         break
 209                 }
 210         }
 211 }