Leetcode 946. Validate Stack Sequences 验证栈序列

946. Validate Stack Sequences

题目描述

Given two sequences pushed and popped with distinct values, return true if and only if this could have been the result of a sequence of push and pop operations on an initially empty stack.

示例

示例1

Input: pushed = [1,2,3,4,5], popped = [4,5,3,2,1]
Output: true
Explanation: We might do the following sequence:
push(1), push(2), push(3), push(4), pop() -> 4,
push(5), pop() -> 5, pop() -> 3, pop() -> 2, pop() -> 1

示例2

Input: pushed = [1,2,3,4,5], popped = [4,3,5,1,2]
Output: false
Explanation: 1 cannot be popped before 2.

解答

这道题很简单，把pushed数组里面的每个数字入栈，然后当push的值和popped里面的第一个未处理的值相等的时候，就进入循环，将popped数组里面的值从栈中移除。

最后判断popped数组里面的值是否处理完。

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class { public: bool validateStackSequences(vector<int>& pushed, vector<int>& popped) { stack<int> mystack; int i = 0; for (auto &s : pushed) { mystack.push(s); while (!mystack.empty() && mystack.top() == popped[i]) { i ++; mystack.pop(); } } if (mystack.empty() && i == popped.size()){ return true; } return false; } };