20.有效的括号

#include <unordered_map>
unordered_map<int,int> Hash = 
{
{')', '('},
{']', '['},
{'}', '{'}
};

class Solution {
public:
    bool isValid(string s) {
        int n = s.size();
        if (n % 2 == 1) {
            return false;
        }
        unordered_map<char, char> pairs = {
            {')', '('},
            {']', '['},
            {'}', '{'}
        };
        stack<char> stk;
        for (char ch: s) {
            if (pairs.count(ch)) {
                if (stk.empty() || stk.top() != pairs[ch]) {
                    return false;
                }
                stk.pop();
            }
            else {
                stk.push(ch);
            }
        }
        return stk.empty();
    }
};