数据结构C#版笔记--堆栈(Stack)

堆栈(Stack)最明显的特征就是“先进后出”，本质上讲堆栈也是一种线性结构，符合线性结构的基本特点：即每个节点有且只有一个前驱节点和一个后续节点。

相对前面学习过的顺序表、链表不同的地方在于：Stack把所有操作限制在"只能在线性结构的某一端"进行，而不能在中间插入或删除元素。下面是示意图：

从示意图中可以看出，堆栈有二种实现方式：基于数组的顺序堆栈实现、类似链表的链式堆栈实现

先抽象堆栈的接口IStack:

namespace 栈与队列
{public interface IStack<T>{/// <summary>/// 返回堆栈的实际元素个数/// </summary>/// <returns></returns>int Count();/// <summary>/// 判断堆栈是否为空/// </summary>/// <returns></returns>bool IsEmpty();/// <summary>/// 清空堆栈里的元素/// </summary>void Clear();/// <summary>/// 入栈：将元素压入堆栈中/// </summary>/// <param name="item"></param>void Push(T item);/// <summary>/// 出栈：从堆栈顶取一个元素，并从堆栈中删除/// </summary>/// <returns></returns>T Pop();/// <summary>/// 取堆栈顶部的元素(但不删除)/// </summary>/// <returns></returns>T Peek();}
}

顺序堆栈(SeqStack)的实现：

using System;
using System.Text;namespace 栈与队列
{public class SeqStack<T>:IStack<T>{private int maxsize;private T[] data;private int top;        public SeqStack(int size) {data = new T[size];maxsize = size;top = -1;}#region //接口实现部分public int Count() {return top + 1;}public void Clear() {top = -1;}public bool IsEmpty() {return top == -1;}public void Push(T item){if (IsFull()){Console.WriteLine("Stack is full");return;}data[++top] = item;}public T Pop(){T tmp = default(T);if (IsEmpty()){Console.WriteLine("Stack is empty");return tmp;}tmp = data[top];top--;return tmp;}public T Peek(){if (IsEmpty()){Console.WriteLine("Stack is empty!");return default(T);}return data[top];}#endregionpublic bool IsFull() {return top == maxsize - 1;}public override string ToString(){StringBuilder sb = new StringBuilder();for (int i = top;i>=0;i--){sb.Append(data[i] + ",");}return sb.ToString().Trim(',');}        }
}

链式堆栈(LinkStack)的实现

先定义节点Node.cs

namespace 栈与队列
{public class Node<T>{private T data;private Node<T> next;public Node(T data, Node<T> next) {this.data = data;this.next = next;}public Node(Node<T> next) {this.next = next;this.data = default(T);}public Node(T data) {this.data = data;this.next = null;}public Node() {this.data = default(T);this.next = null;}public T Data {get { return this.data; }set { this.data = value; }}public Node<T> Next {get { return next; }set { next = value; }}}
}

下面是LinkStack.cs

using System;
using System.Text;namespace 栈与队列
{public class LinkStack<T>:IStack<T>{private Node<T> top;private int num;//节点个数/// <summary>/// 顶部节点/// </summary>public Node<T> Top {get { return top; }set { top = value; }}public LinkStack() {top = null;num = 0;}public int Count() {return num;}public void Clear() {top = null;num = 0;}public bool IsEmpty() {if (top == null && num == 0){return true;}else {return false;}}public void Push(T item) {Node<T> q = new Node<T>(item);if (top == null){top = q;}else {q.Next = top;top = q;}num++;}public T Pop() {if (IsEmpty()) {Console.WriteLine("Stack is empty!");return default(T);}Node<T> p = top;top = top.Next;num--;return p.Data;}public T Peek() {if (IsEmpty()) {Console.WriteLine("Stack is empty!");return default(T);}return top.Data;}public override string ToString(){StringBuilder sb = new StringBuilder();if (top != null) {sb.Append(top.Data.ToString() + ",");Node<T> p = top;while (p.Next != null){                    sb.Append(p.Next.Data.ToString()+ ",");p = p.Next;}}return sb.ToString();}}
}

测试代码片段：

            Console.WriteLine("顺序堆栈测试开始...");SeqStack<int> seqStack = new SeqStack<int>(10);seqStack.Push(1);seqStack.Push(2);seqStack.Push(3);Console.WriteLine(seqStack);Console.WriteLine(seqStack.Peek());Console.WriteLine(seqStack);Console.WriteLine(seqStack.Pop());Console.WriteLine(seqStack);Console.WriteLine("链堆栈测试开始...");LinkStack<int> linkStack = new LinkStack<int>();linkStack.Push(1);linkStack.Push(2);linkStack.Push(3);Console.WriteLine(linkStack);Console.WriteLine(linkStack.Peek());Console.WriteLine(linkStack);Console.WriteLine(linkStack.Pop());Console.WriteLine(linkStack);Console.ReadLine();

.Net中System.Collections.Generic.Stack<T>已经提供了堆栈的基本实现，明白原理后，仍然推荐大家使用内置的实现。