数据结构学习笔记——stack实现（数组篇）

一 栈：是一种表，限制插入和删除只能在一个位置，也即是表的末端（也是栈的顶）进行。

      基本操作：push 和 pop。

二 栈的数组实现：

      运用数组来存储元素，和栈操作先关的是theArray（一个数组实例）和topOfStack（指向栈顶元素，对于空栈，它的值是-1）。

      push操作：将某个元素 item 推入栈中，使得 topOfStack 增1然后置 theArray[topOfStack] = item.

      pop操作： 将栈顶严肃弹出，我们置返回值为 theArray[topOfStack]，然后 topOfStack 减1.

三 时间复杂度：

     显然都是常数时间运行，O(1)。

java代码实现：

package com.xuyunyu.demo;
/**
 * 
 * generic type class MyStack to implement the stack with array
 * @author Administrator
 *
 * @param <AnyType>
 */
public class MyStack<AnyType>
{
    /**
     * the capacity of the stack
     */
    private static  final int DEFAULT_CAPACITY = 10;
    /**
     * the array to store the elements
     */
    private AnyType[] theItems;
    /**
     * the pointer to point to the top of the stack
     */
    private int TopOfStack;
    /**
     * constructor
     * 
     * to initial the stack
     */
    public MyStack ()
    {
        clear();
    }
    /**
     * clear the stack
     */
    public void clear()
    {
        theItems = ( AnyType [] ) new Object[DEFAULT_CAPACITY];
        TopOfStack = -1;
    }
    /**
     * get the capacity of the stack
     * @return
     */
    public int size()
    {
        return DEFAULT_CAPACITY;
    }
    /**
     * get the actual counts of 
     * the element stored in the stack
     * @return
     */
    public int getCountOfElement()
    {
        return TopOfStack + 1;
    }
    /**
     * get the top element of the stack
     * @return
     */
    public AnyType getTopElement()
    {
        return theItems[TopOfStack];
    }
    /**
     * judge if the stack is empty
     * @return true if the stack is empty,false or not
     */
    public boolean isEmpty()
    {
        return TopOfStack == -1;
    }
    /**
     * judge if the stack is full
     * @return true if the stack is full,false or not 
     */
    public boolean isFull()
    {
        return (TopOfStack + 1) == theItems.length;
    }
    /**
     * push an item to the stack
     * the TopOfStack INC ,and then store the item
     * @param item
     */
    public void push(AnyType item)
    {
        if(isFull())
            throw new IndexOutOfBoundsException();        
        TopOfStack++;
        theItems[TopOfStack] = item;
    }
    /**
     * return the item on the top and then make one decrement of the TopOfStack
     * @return
     */
    public AnyType pop()
    {
        if(isEmpty() )
            throw new IndexOutOfBoundsException();
        
        AnyType ItemPulled = theItems[TopOfStack];
        theItems[TopOfStack] = null;
        TopOfStack--;        
        return ItemPulled;
    }
    
    

}

注意：这是一个泛型类，更加具有复用性。

四 测试代码：

package com.xuyunyu.demo;


public class test_MyStack
{
    public static void main(String[] args)
    {
        MyStack<Integer> stack = new MyStack<Integer>();
        System.out.println("counts of the stack: " + stack.getCountOfElement());
        System.out.println("size of the stack: " + stack.size());
        //System.out.println("top element of the stack: " + stack.getTopElement());
        
        stack.push(17);
        System.out.println("counts of the stack: " + stack.getCountOfElement());
        System.out.println("top element of the stack: " + stack.getTopElement());
        
        stack.push(30);
        System.out.println("counts of the stack: " + stack.getCountOfElement());
        System.out.println("top element of the stack: " + stack.getTopElement());
        
        stack.clear();
        System.out.println("counts of the stack: " + stack.getCountOfElement());
        
        System.out.println("push to the stack:" );
        for (int i = 0; i < stack.size(); i++)
        {    
            System.out.print(" " + i);
            stack.push(i);
        }
        System.out.println();
        
        System.out.println("pop from the stack:" );
        for (int i = 0; i < stack.size(); i++)
        {
            System.out.print(" " + stack.pop());
        }
        
    }

}

期待输出如下：

counts of the stack: 0
size of the stack: 10
counts of the stack: 1
top element of the stack: 17
counts of the stack: 2
top element of the stack: 30
counts of the stack: 0
push to the stack
 0 1 2 3 4 5 6 7 8 9
pop from the stack
 9 8 7 6 5 4 3 2 1 0

结论：

显然实现了stack的后进先出的性质。

栈可以应用到平衡符号，中缀到后缀的转换以及方法调用上。详情可参考Mark Allen Weisss的《数据结构与算法分析——java语言描述》。 本文部分内容页参考此书。