解法：

#include<iostream>
#include<vector>
#include<string>
using namespace std;
int arr[100][100];
string vertex;
void dfs(vector<int>& a,int u) {
	a[u] = 1;
	cout << vertex[u];
	for (int i = 0; i < a.size(); i++) {
		if (arr[u][i] && !a[i]) {
			dfs(a, i);
		}
	}
}
int main() {
	int n;
	cin >> n;
	vector<int> vis(n, 0);
	cin >> vertex;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> arr[i][j];
		}
	}
	char x;
	cin >> x;
	int pos;
	for (pos = 0; pos < vertex.size(); pos++) {
		if (x == vertex[pos])
			break;
	}
	dfs(vis, pos);
	return 0;
}