list底层数据结构为双向链表（双向链表）

本文实例讲述了C#数据结构之双向链表(DbLinkList)。分享给大家供大家参考，具体如下：

这是继上一篇《C#数据结构之单链表(LinkList)实例详解》的继续，对于双向链接，节点上除了Next属性外，还要有Prev属性用来指向前一个节点，DbNode定义如下：

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namespace 线性表 { public class DbNode<T> { private T data; private DbNode<T> prev; private DbNode<T> next; public DbNode(T data, DbNode<T> next,DbNode<T> prev) { this.data = data; this.next = next; this.prev = prev; } public DbNode(T data, DbNode<T> next) { this.data = data; this.next = next; this.prev = null; } public DbNode(DbNode<T> next) { this.data = default(T); this.next = next; this.prev = null; } public DbNode(T data) { this.data = data; this.next = null; this.prev = null; } public DbNode() { data = default(T); next = null; prev = null; } public T Data { set { this.data = value; } get { return this.data; } } public DbNode<T> Prev { get { return prev; } set { prev = value; } } public DbNode<T> Next { get { return next; } set { next = value; } } } }

双链表的插入操作要稍微复杂一点，示意图如下：

同样对于删除操作，也要额外处理prev指向

完整实现DbLinkList<T>：

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using System; using System.Text; namespace 线性表 { public class DbLinkList<T> : IListDS<T> { private DbNode<T> head; public DbNode<T> Head { get { return head; } set { head = value; } } public DbLinkList() { head = null; } /// <summary> /// 类索引器 /// </summary> /// <param name="index"></param> /// <returns></returns> public T this[int index] { get { return this.GetItemAt(index); } } /// <summary> /// 返回单链表的长度 /// </summary> /// <returns></returns> public int Count() { DbNode<T> p = head; int len = 0; while (p != null) { len++; p = p.Next; } return len; } /// <summary> /// 清空 /// </summary> public void Clear() { head = null; } /// <summary> /// 是否为空 /// </summary> /// <returns></returns> public bool IsEmpty() { return head == null; } /// <summary> /// 在最后附加元素 /// </summary> /// <param name="item"></param> public void Append(T item) { DbNode<T> d = new DbNode<T>(item); DbNode<T> n = new DbNode<T>(); if (head == null) { head = d; return; } n = head; while (n.Next != null) { n = n.Next; } n.Next = d; d.Prev = n; } //前插 public void InsertBefore(T item, int i) { if (IsEmpty() || i < 0) { Console.WriteLine("List is empty or Position is error!"); return; } //在最开头插入 if (i == 0) { DbNode<T> q = new DbNode<T>(item); q.Next = head;//把"头"改成第二个元素 head.Prev = q; head = q;//把自己设置为"头" return; } DbNode<T> n = head; DbNode<T> d = new DbNode<T>(); int j = 0; //找到位置i的前一个元素d while (n.Next != null && j < i) { d = n; n = n.Next; j++; } if (n.Next == null) //说明是在最后节点插入(即追加) { DbNode<T> q = new DbNode<T>(item); n.Next = q; q.Prev = n; q.Next = null; } else { if (j == i) { DbNode<T> q = new DbNode<T>(item); d.Next = q; q.Prev = d; q.Next = n; n.Prev = q; } } } /// <summary> /// 在位置i后插入元素item /// </summary> /// <param name="item"></param> /// <param name="i"></param> public void InsertAfter(T item, int i) { if (IsEmpty() || i < 0) { Console.WriteLine("List is empty or Position is error!"); return; } if (i == 0) { DbNode<T> q = new DbNode<T>(item); q.Next = head.Next; head.Next.Prev = q; head.Next = q; q.Prev = head; return; } DbNode<T> p = head; int j = 0; while (p != null && j < i) { p = p.Next; j++; } if (j == i) { DbNode<T> q = new DbNode<T>(item); q.Next = p.Next; if (p.Next != null) { p.Next.Prev = q; } p.Next = q; q.Prev = p; } else { Console.WriteLine("Position is error!"); } } /// <summary> /// 删除位置i的元素 /// </summary> /// <param name="i"></param> /// <returns></returns> public T RemoveAt(int i) { if (IsEmpty() || i < 0) { Console.WriteLine("Link is empty or Position is error!"); return default(T); } DbNode<T> q = new DbNode<T>(); if (i == 0) { q = head; head = head.Next; head.Prev = null; return q.Data; } DbNode<T> p = head; int j = 0; while (p.Next != null && j < i) { j++; q = p; p = p.Next; } if (j == i) { p.Next.Prev = q; q.Next = p.Next; return p.Data; } else { Console.WriteLine("The node is not exist!"); return default(T); } } /// <summary> /// 获取指定位置的元素 /// </summary> /// <param name="i"></param> /// <returns></returns> public T GetItemAt(int i) { if (IsEmpty()) { Console.WriteLine("List is empty!"); return default(T); } DbNode<T> p = new DbNode<T>(); p = head; if (i == 0) { return p.Data; } int j = 0; while (p.Next != null && j < i) { j++; p = p.Next; } if (j == i) { return p.Data; } else { Console.WriteLine("The node is not exist!"); return default(T); } } //按元素值查找索引 public int IndexOf(T value) { if (IsEmpty()) { Console.WriteLine("List is Empty!"); return -1; } DbNode<T> p = new DbNode<T>(); p = head; int i = 0; while (!p.Data.Equals(value) && p.Next != null) { p = p.Next; i++; } return i; } /// <summary> /// 元素反转 /// </summary> public void Reverse() { DbLinkList<T> result = new DbLinkList<T>(); DbNode<T> t = this.head; result.Head = new DbNode<T>(t.Data); t = t.Next; //(把当前链接的元素从head开始遍历，逐个插入到另一个空链表中，这样得到的新链表正好元素顺序跟原链表是相反的) while (t!=null) { result.InsertBefore(t.Data, 0); t = t.Next; } this.head = result.head;//将原链表直接挂到"反转后的链表"上 result = null;//显式清空原链表的引用，以便让GC能直接回收 } //得到某个指定的节点(为了下面测试从后向前遍历) private DbNode<T> GetNodeAt(int i){ if (IsEmpty()) { Console.WriteLine("List is empty!"); return null; } DbNode<T> p = new DbNode<T>(); p = head; if (i == 0) { return p; } int j = 0; while (p.Next != null && j < i) { j++; p = p.Next; } if (j == i) { return p; } else { Console.WriteLine("The node is not exist!"); return null; } } /// <summary> /// 测试用prev属性从后面开始遍历 /// </summary> /// <returns></returns> public string TestPrevErgodic() { DbNode<T> tail = GetNodeAt(Count() - 1); StringBuilder sb = new StringBuilder(); sb.Append(tail.Data.ToString() + ","); while (tail.Prev != null) { sb.Append(tail.Prev.Data.ToString() + ","); tail = tail.Prev; } return sb.ToString().TrimEnd(','); } public override string ToString() { StringBuilder sb = new StringBuilder(); DbNode<T> n = this.head; sb.Append(n.Data.ToString() + ","); while (n.Next != null) { sb.Append(n.Next.Data.ToString() + ","); n = n.Next; } return sb.ToString().TrimEnd(','); } } }

测试代码片段：

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Console.WriteLine("-------------------------------------"); Console.WriteLine("双链表测试开始..."); DbLinkList<string> dblink = new DbLinkList<string>(); dblink.Head = new DbNode<string>("x"); dblink.InsertBefore("w", 0); dblink.InsertBefore("v", 0); dblink.Append("y"); dblink.InsertBefore("z", dblink.Count()); Console.WriteLine(dblink.Count());//5 Console.WriteLine(dblink.ToString());//v,w,x,y,z Console.WriteLine(dblink[1]);//w Console.WriteLine(dblink[0]);//v Console.WriteLine(dblink[4]);//z Console.WriteLine(dblink.IndexOf("z"));//4 Console.WriteLine(dblink.RemoveAt(2));//x Console.WriteLine(dblink.ToString());//v,w,y,z dblink.InsertBefore("x", 2); Console.WriteLine(dblink.ToString());//v,w,x,y,z Console.WriteLine(dblink.GetItemAt(2));//x dblink.Reverse(); Console.WriteLine(dblink.ToString());//z,y,x,w,v dblink.InsertAfter("1", 0); dblink.InsertAfter("2", 1); dblink.InsertAfter("6", 5); dblink.InsertAfter("8", 7); dblink.InsertAfter("A", 10);//Position is error! Console.WriteLine(dblink.ToString()); //z,1,2,y,x,w,6,v,8 string _tail = dblink.GetItemAt(dblink.Count()-1); Console.WriteLine(_tail); Console.WriteLine(dblink.TestPrevErgodic());//8 Console.ReadKey(); //8,v,6,w,x,y,2,1,z

当然从上面的测试代码中，似乎并不能看出双链表的优点，双链表的好处在于，如果需要在链表中，需要通过某个节点得到它的前驱节点时，双链表直接用prev属性就能找到；而单链表要做到这一点，必须再次从Head节点开始一个一个用Next向下找，这样时间复杂度从O(n)降到O(1)，显然更有效率。

注：如果把双链表再做一下改造，让头尾接起来，即Head的Prev属性指向最后一个节点(就叫做Tail吧)，同时把Tail节点的Next属性指向Head节点，就形成了所谓的“循环双向链表”

当然，这样的结构可以在链表中再增加一个Tail节点属性，在做元素插入或删除时，可以循环到底以更新尾节点Tail(当然这样会给插入/删除元素带来一些额外的开销)，但是却可以给GetItemAt(int i)方法带来优化的空间，比如要查找的元素在前半段时，可以从Head开始用next向后找；反之，如果要找的元素在后半段，则可以从Tail节点用prev属性向前找。

注：.Net中微软已经给出了一个内置的双向链表System.Collections.Generic.LinkedList<T>，在了解双链表的原理后，建议大家直接系统内置的链表。

希望本文所述对大家C#程序设计有所帮助。