E0087.cpp

/*
Problem Statement: https://www.hackerrank.com/challenges/grid-challenge/problem
*/

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

string gridChallenge(vector<string> grid) {
	for (int i = 0; i < grid.size(); i++)
		sort(grid[i].begin(), grid[i].end());
	for (int i = 0; i < grid.size(); i++)
		for (int j = 1; j < grid.size(); j++)
			if (grid[j - 1][i] > grid[j][i])
				return "NO";
	return "YES";
}

int main() {
	int t;
	cin >> t;
	while (t--) {
		int n;
		cin >> n;
		vector<string> grid(n);
		for (int i = 0; i < n; i++)
			cin >> grid[i];
		cout << gridChallenge(grid) << endl;
	}
	return 0;
}