题目描述(Easy)

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.

题目链接

https://leetcode.com/problems/valid-parentheses/description/

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

算法分析

遇见左括号则入栈，遇见右括号则与栈顶比较是否为一对，并出栈。

提交代码：

class Solution {
public:
    bool isValid(string s) {
        string left = "([{";
        string right = ")]}";
        stack<char> sta;
        
        for(auto c : s)
        {
            if(left.find(c) != string::npos)
                sta.push(c);
            else
            {
                if(sta.empty() || sta.top() != left[right.find(c)])
                    return false;
                sta.pop();
            }
        }
        
        return sta.empty();
    }
};