20. Valid Parentheses

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

An input string is valid if:

1. Open brackets must be closed by the same type of brackets.
2. Open brackets must be closed in the correct order.

Note that an empty string is also considered valid.

Example 1:

Input: "()"
Output: true

Example 2:

Input: "()[]{}"
Output: true

Example 3:

Input: "(]"
Output: false

Example 4:

Input: "([)]"
Output: false

Example 5:

Input: "{[]}"
Output: true

---

判断一个带括号的字符串是否合法，直接用栈，水题，代码如下。

class Solution {
public:
    bool isValid(string s)
    {
        stack<char> pars;
        for (int i = 0; i < s.size(); i++) {
            if (pars.empty()) {
                pars.push(s[i]);
                continue;
            }
            char t = pars.top();
            if ((t == ‘(‘&& s[i] == ‘)’) || (t == ‘{ ‘&& s[i] == ‘ }’) || (t == ‘[‘&& s[i] == ‘]’))
                pars.pop();
            else
                pars.push(s[i]);
        }
        return pars.empty();
    }
};

本代码提交AC，用时0MS。