UVa 10008 - What's Cryptanalysis?

// UVa 10008 - What's Cryptanalysis?
#include <iostream>
#include <vector>
#include <algorithm>
#include <string.h>
#include <stdio.h>
using namespace std;

struct pa {
	char c;
	unsigned long long int f;
};

bool operator <(pa a, pa b) {
	return a.f > b.f || a.f == b.f && a.c < b.c;
}

int main() {
	int n;
	cin >> n;
	string l;
	getline(cin, l);
	unsigned long long int m[26];
	memset(m, 0, sizeof(m));
	for (; n; n--) {
		getline(cin, l);
		for (int i = 0; i < l.length(); i++) {
			if (l[i] >= 'a' && l[i] <= 'z')
				l[i] = l[i] - 'a' + 'A';
			if (l[i] >= 'A' && l[i] <= 'Z')
				m[l[i] - 'A']++;
		}
	}
	vector<pa> v;
	for (char ch = 0; ch < 26; ch++)
		if (m[ch] > 0) {
			pa p = { ch, m[ch] };
			v.push_back(p);
		}
	sort(v.begin(), v.end());
	for (int i = 0; i < v.size(); i++)
		printf("%c %llu\n", v[i].c + 'A', v[i].f);
	return 0;
}