LeetCode20. Valid Parentheses

题目：

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

题目分析：

很简单的一道题，在大二的时候就已经做过了很多次了，就是简单的括号匹配，用栈去模拟。

代码：

#include<iostream>]#include<stack>#include<string>using namespace std;class Solution {public:bool isValid(string s) {stack<char> stack;for (int i = 0; i < s.size(); i++) {if (s[i] == '{' || s[i] == '[' || s[i] == '(') {stack.push(s[i]);}else if (s[i] == '}' || s[i] == ']' || s[i] == ')') {if (stack.empty()) {return false;}else {if (stack.top() != pipei(s[i])) {return false;}else {stack.pop();}}}}if (!stack.empty()) {return false;}return true;}    char pipei(char a) {if (a == '}') {return '{';}else if (a == ']') {return '[';}else if (a == ')') {return '(';}return ' ';    }};