题目：

题解：

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();}
};