题解 | #栈的压入、弹出序列#

import java.util.*;

public class Solution {
    public boolean IsPopOrder(int [] pushA,int [] popA) {
        if(pushA.length == 0 || popA.length == 0 || pushA.length != popA.length)return false;
        Stack<Integer> help = new Stack<Integer>();
        int j = 0;//一开始就要初始化内循环的循环变量，后面要先用
        for(int i = 0;i < pushA.length;i++){
            help.push(pushA[i]);
            while(!help.isEmpty() && help.peek() == popA[j]){
                //这里注意逻辑的先后顺序，先保证辅助栈不为空在执行peek操作
                help.pop();//执行辅助栈的弹栈
                j++;//并且让j加一
            }
        }
        return help.isEmpty();
    }
}