2.8 栈

图例

• 盒子最上面的元素称为栈顶元素

代码演示：

MyStack.java类

package com.kami.leetcode.alg_stack;

public class MyStack {

    //栈的底层我们用数组来存储数据
    int[] elements;

    public MyStack(){
        elements = new int[0];
    }

    //压入元素
    public void push(int element){
        int[] newArr = new int[elements.length + 1];

        for(int i = 0; i < elements.length; i++){
            newArr[i] = elements[i];
        }
        newArr[elements.length] = element;

        elements = newArr;
    }

    //取出栈顶元素
    public int pop(){
        if(elements.length == 0){
            throw new RuntimeException("stack is empty");
        }
        //取出最后一个元素
        int element = elements[elements.length - 1];
        //创建新数组
        int[] newArr = new int[elements.length - 1];
        //原数组中除了最后一个元素，其他元素放到新的数组当中
        for(int i = 0; i < elements.length - 1; i++){
            newArr[i] = elements[i];
        }
        //替换数组
        elements = newArr;
        //返回栈顶元素
        return element;
    }

    //查看栈顶元素
    public int peek(){
        //栈中有没有元素
        if(elements.length == 0){
            throw new RuntimeException("stack is empty");
        }
        return elements[elements.length - 1];
    }

    //判断栈是否为空
    public boolean isEmpty(){
        return elements.length == 0 ? true : false;
    }
}

testMyStack.java测试类

package com.kami.leetcode.alg_stack.test;

import com.kami.leetcode.alg_stack.MyStack;

public class testMyStack {
    public static void main(String[] args) {
        //创建一个栈
        MyStack myStack = new MyStack();
        //压入数组
        myStack.push(9);
        myStack.push(7);
        myStack.push(8);
        //取出栈顶元素
        System.out.println(myStack.pop());
        //查看栈顶元素
        System.out.println(myStack.peek());
        //判断是否为空
        System.out.println(myStack.isEmpty());
    }
}