UVa 11577 - Letter Frequency

// UVa 11577 - Letter Frequency
#include <iostream>
#include <string>
#include <string.h>
using namespace std;

int main() {
	int t;
	cin >> t;
	string line;
	getline(cin, line);
	for (; t; t--) {
		getline(cin, line);

		int f[256];
		memset(f, 0, sizeof(f));
		int mx = -1;
		for (int i = 0; i < line.length(); i++) {
			if (line[i] >= 'A' && line[i] <= 'Z')
				line[i] = line[i] + ('a' - 'A');
			if (line[i] >= 'a' && line[i] <= 'z') {
				f[line[i]]++;
				if (f[line[i]] > mx)
					mx = f[line[i]];
			}
		}
		for (char c = 'a'; c <= 'z'; c++)
			if (f[c] == mx)
				cout << c;
		cout << endl;
	}
	return 0;
}