github.com/sagernet/sing@v0.4.0-beta.19.0.20240518125136-f67a0988a636/common/x/list/list.go (about)

     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  // Package list implements a doubly linked list.
     6  //
     7  // To iterate over a list (where l is a *List[T]):
     8  //
     9  //	for e := l.Front(); e != nil; e = e.Next() {
    10  //		// do something with e.Value
    11  //	}
    12  package list
    13  
    14  // Element is an element of a linked list.
    15  type Element[T any] struct {
    16  	// Next and previous pointers in the doubly-linked list of elements.
    17  	// To simplify the implementation, internally a list l is implemented
    18  	// as a ring, such that &l.root is both the next element of the last
    19  	// list element (l.Back()) and the previous element of the first list
    20  	// element (l.Front()).
    21  	next, prev *Element[T]
    22  
    23  	// The list to which this element belongs.
    24  	list *List[T]
    25  
    26  	// The value stored with this element.
    27  	Value T
    28  }
    29  
    30  // Next returns the next list element or nil.
    31  func (e *Element[T]) Next() *Element[T] {
    32  	if p := e.next; e.list != nil && p != &e.list.root {
    33  		return p
    34  	}
    35  	return nil
    36  }
    37  
    38  // Prev returns the previous list element or nil.
    39  func (e *Element[T]) Prev() *Element[T] {
    40  	if p := e.prev; e.list != nil && p != &e.list.root {
    41  		return p
    42  	}
    43  	return nil
    44  }
    45  
    46  // List represents a doubly linked list.
    47  // The zero value for List is an empty list ready to use.
    48  type List[T any] struct {
    49  	root Element[T] // sentinel list element, only &root, root.prev, and root.next are used
    50  	len  int        // current list length excluding (this) sentinel element
    51  }
    52  
    53  // Init initializes or clears list l.
    54  func (l *List[T]) Init() *List[T] {
    55  	l.root.next = &l.root
    56  	l.root.prev = &l.root
    57  	l.len = 0
    58  	return l
    59  }
    60  
    61  // Len returns the number of elements of list l.
    62  // The complexity is O(1).
    63  func (l *List[T]) Len() int { return l.len }
    64  
    65  // Front returns the first element of list l or nil if the list is empty.
    66  func (l *List[T]) Front() *Element[T] {
    67  	if l.len == 0 {
    68  		return nil
    69  	}
    70  	return l.root.next
    71  }
    72  
    73  // Back returns the last element of list l or nil if the list is empty.
    74  func (l *List[T]) Back() *Element[T] {
    75  	if l.len == 0 {
    76  		return nil
    77  	}
    78  	return l.root.prev
    79  }
    80  
    81  // lazyInit lazily initializes a zero List value.
    82  func (l *List[T]) lazyInit() {
    83  	if l.root.next == nil {
    84  		l.Init()
    85  	}
    86  }
    87  
    88  // insert inserts e after at, increments l.len, and returns e.
    89  func (l *List[T]) insert(e, at *Element[T]) *Element[T] {
    90  	e.prev = at
    91  	e.next = at.next
    92  	e.prev.next = e
    93  	e.next.prev = e
    94  	e.list = l
    95  	l.len++
    96  	return e
    97  }
    98  
    99  // insertValue is a convenience wrapper for insert(&Element{Value: v}, at).
   100  func (l *List[T]) insertValue(v any, at *Element[T]) *Element[T] {
   101  	e := new(Element[T])
   102  	e.Value = v.(T)
   103  	return l.insert(e, at)
   104  }
   105  
   106  // remove removes e from its list, decrements l.len
   107  func (l *List[T]) remove(e *Element[T]) {
   108  	e.prev.next = e.next
   109  	e.next.prev = e.prev
   110  	e.next = nil // avoid memory leaks
   111  	e.prev = nil // avoid memory leaks
   112  	e.list = nil
   113  	l.len--
   114  }
   115  
   116  // move moves e to next to at.
   117  func (l *List[T]) move(e, at *Element[T]) {
   118  	if e == at {
   119  		return
   120  	}
   121  	e.prev.next = e.next
   122  	e.next.prev = e.prev
   123  
   124  	e.prev = at
   125  	e.next = at.next
   126  	e.prev.next = e
   127  	e.next.prev = e
   128  }
   129  
   130  // Remove removes e from l if e is an element of list l.
   131  // It returns the element value e.Value.
   132  // The element must not be nil.
   133  func (l *List[T]) Remove(e *Element[T]) T {
   134  	if e.list == l {
   135  		// if e.list == l, l must have been initialized when e was inserted
   136  		// in l or l == nil (e is a zero Element) and l.remove will crash
   137  		l.remove(e)
   138  	}
   139  	return e.Value
   140  }
   141  
   142  // PushFront inserts a new element e with value v at the front of list l and returns e.
   143  func (l *List[T]) PushFront(v T) *Element[T] {
   144  	l.lazyInit()
   145  	return l.insertValue(v, &l.root)
   146  }
   147  
   148  // PushBack inserts a new element e with value v at the back of list l and returns e.
   149  func (l *List[T]) PushBack(v T) *Element[T] {
   150  	l.lazyInit()
   151  	return l.insertValue(v, l.root.prev)
   152  }
   153  
   154  // InsertBefore inserts a new element e with value v immediately before mark and returns e.
   155  // If mark is not an element of l, the list is not modified.
   156  // The mark must not be nil.
   157  func (l *List[T]) InsertBefore(v T, mark *Element[T]) *Element[T] {
   158  	if mark.list != l {
   159  		return nil
   160  	}
   161  	// see comment in List.Remove about initialization of l
   162  	return l.insertValue(v, mark.prev)
   163  }
   164  
   165  // InsertAfter inserts a new element e with value v immediately after mark and returns e.
   166  // If mark is not an element of l, the list is not modified.
   167  // The mark must not be nil.
   168  func (l *List[T]) InsertAfter(v T, mark *Element[T]) *Element[T] {
   169  	if mark.list != l {
   170  		return nil
   171  	}
   172  	// see comment in List.Remove about initialization of l
   173  	return l.insertValue(v, mark)
   174  }
   175  
   176  // MoveToFront moves element e to the front of list l.
   177  // If e is not an element of l, the list is not modified.
   178  // The element must not be nil.
   179  func (l *List[T]) MoveToFront(e *Element[T]) {
   180  	if e.list != l || l.root.next == e {
   181  		return
   182  	}
   183  	// see comment in List.Remove about initialization of l
   184  	l.move(e, &l.root)
   185  }
   186  
   187  // MoveToBack moves element e to the back of list l.
   188  // If e is not an element of l, the list is not modified.
   189  // The element must not be nil.
   190  func (l *List[T]) MoveToBack(e *Element[T]) {
   191  	if e.list != l || l.root.prev == e {
   192  		return
   193  	}
   194  	// see comment in List.Remove about initialization of l
   195  	l.move(e, l.root.prev)
   196  }
   197  
   198  // MoveBefore moves element e to its new position before mark.
   199  // If e or mark is not an element of l, or e == mark, the list is not modified.
   200  // The element and mark must not be nil.
   201  func (l *List[T]) MoveBefore(e, mark *Element[T]) {
   202  	if e.list != l || e == mark || mark.list != l {
   203  		return
   204  	}
   205  	l.move(e, mark.prev)
   206  }
   207  
   208  // MoveAfter moves element e to its new position after mark.
   209  // If e or mark is not an element of l, or e == mark, the list is not modified.
   210  // The element and mark must not be nil.
   211  func (l *List[T]) MoveAfter(e, mark *Element[T]) {
   212  	if e.list != l || e == mark || mark.list != l {
   213  		return
   214  	}
   215  	l.move(e, mark)
   216  }
   217  
   218  // PushBackList inserts a copy of another list at the back of list l.
   219  // The lists l and other may be the same. They must not be nil.
   220  func (l *List[T]) PushBackList(other *List[T]) {
   221  	l.lazyInit()
   222  	for i, e := other.Len(), other.Front(); i > 0; i, e = i-1, e.Next() {
   223  		l.insertValue(e.Value, l.root.prev)
   224  	}
   225  }
   226  
   227  // PushFrontList inserts a copy of another list at the front of list l.
   228  // The lists l and other may be the same. They must not be nil.
   229  func (l *List[T]) PushFrontList(other *List[T]) {
   230  	l.lazyInit()
   231  	for i, e := other.Len(), other.Back(); i > 0; i, e = i-1, e.Prev() {
   232  		l.insertValue(e.Value, &l.root)
   233  	}
   234  }