此题题解

1.栈的方法：

#include <bits/stdc++.h>
#define MOD 998244353
#define mod 1000000007
using namespace std;
int main()
{
	stack<char>s;
    string str;
    cin >> str;
    for (int i = 0; str[i] != '@'; i++)
    {
        if (str[i] == '(') s.push('(');
        if (str[i] == ')')
        {
            if (s.empty())
            {
                cout << "NO" << endl;
                return 0;
            }
            else s.pop();
        }
    }
    s.empty() ? cout << "YES" << endl : cout << "NO\n";
	return 0;
}

2.统计(和)的个数：

#include <bits/stdc++.h>
using namespace std;
int main()
{
	string s;
	cin >> s;
	int left = 0; 
	int right = 0;
	for (int i = 0; i < s.length(); i++)
	{
		if (s[i] == '(') left++;
		else if (s[i] == ')') right++;
		else if (s[i] == '@') break;
	}
	if (left == right) cout << "YES" << endl;
	else cout << "NO" << endl;
 	return 0;
}

完结！