有效的括号

输入: "()"
输出: true

输入: "()[]{}"
输出: true

输入: "(]"
输出: false

输入: "([)]"
输出: false

输入: "{[]}"
输出: true

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] == '[') {
                stack.push(s[i]);
            } else {
                if (stack.size() == 0) {
                    return false;
                }
                
                char c = stack.top();
                stack.pop();

                char match;
                if(s[i] == ')')
                    match = '(';
                else if(s[i] == ']')
                    match = '[';
                else {
                    assert(s[i] == '}');
                    match = '{';
                }

                if(c != match)
                    return false;
            }
            
        }
        if (stack.size() != 0) {
            return false;
        }
        return true;
    }
};