20. Valid Parentheses

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.

Solution:

class Solution {
public:
    bool isValid(string s) {
        stack<char> m;
        bool r = true;
        for(int i=0;i<s.size();i++){
            if('(' == s[i] || '{' == s[i] || '[' == s[i])
                m.push(s[i]);
            else{
                if(m.empty())
                    return false;
                char x = m.top();
                if(x + 1 == s[i] || x + 2 == s[i]){
                    m.pop();
                }else{
                    r = false;
                    break;
                }
            }
        }
        if(r && m.empty()) return true;
        else return false;
    }
};