题解 100% AC

#include <bits/stdc++.h>
using namespace std;
int TOP;
char a[265],x;
void push(char x){a[++TOP]=x;}
void pop(){--TOP;}
bool empty(){return TOP==0;}
int main(){
    string x;cin>>x;
    for(int i=0;i<x.length();i++){
        if(x[i]=='(') push(x[i]);
        else if(x[i]==')'){
            if(!empty()) pop();
            else{
                cout<<"NO";
                return 0;
            }
        }else if(x[i]=='@') break;
    }
    if(empty()) cout<<"YES";
    else cout<<"NO";
    return 0;
}