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 m;
        bool r = true;
        for(int i=0;i