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

 

class Solution {
public:
    bool isValid(string s) {
        stack<char> sta;
        map<char, char> mp;
        mp['('] = ')'; mp['['] = ']'; mp['{']='}';
        int n = s.size();
        for(int i=0; i<n; i++) {
            if(s[i] == '(' || s[i] == '[' || s[i] == '{')
                sta.push(s[i]);
            if(s[i] == ')' || s[i] == ']' || s[i] == '}')
                if(sta.empty() || s[i] != mp[sta.top()])
                    return false;
                else
                    sta.pop();

        }
        if(sta.empty())
            return true;
        else
            return false;
    }
};