栈

class Solution {
public:
    bool isValid(string s) {
        stack<char>stk;
        for(auto c:s){
            if(c=='(' || c=='{' || c=='[')stk.push(c);
            else{
                if(stk.size() && abs(stk.top()-c)<=2)stk.pop();  //ASCII码
                else return false;
            }
        }
        return stk.empty();
    }
};
//栈