20 有效的括号

https://leetcode.cn/leetbook/read/top-interview-questions-easy/xnbcaj/

https://leetcode.cn/problems/valid-parentheses/description/

cost: 6m34s

class Solution {
public:
    bool isValid(string s) {
        stack<char> mystack;
        for (const char& ch : s) {
            switch (ch) {
            case '(':
                mystack.push(')');
                break;
            case '[':
                mystack.push(']');
                break;
            case '{':
                mystack.push('}');
                break;
            case ')':
            case ']':
            case '}':
                if (mystack.empty()) {
                    return false;
                }
                if (mystack.top() != ch) {
                    return false;
                }
                mystack.pop();
                break;
            default:
            }
        }
        return mystack.empty();
    }
};