LeetCode – Refresh – Valid Parentheses

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