题解 | #栈的压入、弹出序列#

import java.util.*;

public class Solution {
    public boolean IsPopOrder(int [] pushA, int [] popA) {
        Stack<Integer> stack = new Stack<>();
        int flag = 0;
        for (int i = 0; i < pushA.length; i++) {
            //flag < pushA.length用来限制当pushA添加完后只能执行出栈
            //栈顶元素不等于popA元素就入栈
            //flag用来标记入栈元素在pushA的位置
            while (flag < pushA.length && (stack.isEmpty() || stack.peek() != popA[i])) {
                stack.push(pushA[flag]);
                flag++;
            }
            //栈顶等于popA元素就出栈
            if (stack.peek() == popA[i]) {
                stack.pop();
                //不相等说明不可以
            } else {
                return false;
            }
        }

        return true;
    }
}