题解

#include <iostream>
#include <cstdio>
using namespace std;
string a;
bool check(string a){
	int i;
	for(i = 0; a[i] != '\0'; i++){
		if(a[i] != '4' && a[i] != '7') return 0;
	}
	int ct1 = 0, ct2 = 0;
	for(int j = 0; j < i / 2; j++) ct1 += a[j];
	if(i % 2) i++;
	for(int j = i / 2; a[j] != '\0'; j++) ct2 += a[j];
	return ct1 == ct2;
}
int main(){
	int t, n;
	scanf("%d", &t);
	while(t--){
		scanf("%d", &n);
		cin >> a;
		cout << (check(a) ? "YES\n" : "NO\n");
	}

	return 0;
}