题解

#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;

int test(string s)
{
	string ss = "";
	int flag = 0;
	for (int i = 0; i < s.size(); i++)
	{
		if (s[i] != '0')
			flag = 1;
		if (flag)
			ss += s[i];
	}
	if (flag == 0)
		return 0;
	for (int i = 0; i < ss.size(); i++)
		if ((ss[i] != '4') and (ss[i] != '7'))
			return 0;
	int num = 0;
	for (int i = 0; i < ss.size() / 2; i++)
		num += ss[i] - '0';
	int num1 = 0;
	int st = ss.size() / 2;
	if (ss.size() % 2 == 1)
		st++;
	for (int i = st; i < ss.size(); i++)
		num1 += ss[i] - '0';
	if (num != num1)
		return 0;
	return 1;
}

int main()
{
	int t;
	cin >> t;
	while (t--)
	{
		int n;
		cin >> n;
		string s;
		cin >> s;
		if (test(s))
			cout << "YES" << endl;
		else
			cout << "NO" << endl;
	}
	return 0;
}