LeetCode 20. 有效的括号

class Solution {
public:
    bool isValid(string s) {
        stack<char> stack;

        for (int i = 0; i < s.size(); i ++) {
            if (s[i] == ')' || s[i] =='}' || s[i] == ']') {
                if (stack.empty()) return false;

                char temp = stack.top();
                stack.pop();
                if (s[i] == ')' && temp != '(') return false;
                else if (s[i] == '}' && temp != '{') return false;
                else if (s[i] == ']' && temp != '[') return false;
            }

            else stack.push(s[i]);
        }

        return stack.empty();
    }
};