cpp

#define _CRT_SECURE_NO_WARNINGS 1

#include <stdio.h>
#include <string.h>
#include <map>
#include <vector>
#include <set>
#include <algorithm>
#include <iterator>

using namespace std;

map<unsigned long, vector<unsigned long>> load_group_users(char* user_groups_filename)
{
	map<unsigned long, vector<unsigned long>> result;

	// Open file
	auto user_group_file = fopen(user_groups_filename, "r");

	char line_buff[128], user_str[64], group_str[64];
	char * comma_pos;
	size_t line_len, comma_len;
	long user, group;


	// Read file line-by-line
	while (fgets(line_buff, sizeof line_buff, user_group_file) != NULL)
	{
		memset(user_str, 0, sizeof user_str);
		memset(group_str, 0, sizeof group_str);

		line_len = strlen(line_buff);
		comma_pos = strchr(line_buff, ',');
		comma_len = comma_pos - line_buff;

		strncpy(user_str, line_buff, comma_len);
		strncpy(group_str, comma_pos + 1, line_len - comma_len - 2);

		user = atol(user_str);
		group = atol(group_str);

		if (result.find(group) == result.end())
		{
			result[group].reserve(100);
		}
		result[group].push_back(user);

		printf("Load %lu - %lu\n", group, user);
	}
	fclose(user_group_file);

	return result;
};

void calc_and_write_group_shr(map<unsigned long, vector<unsigned long>> group_users_data, char * output_filename)
{
	auto file = fopen(output_filename, "w");


	for (auto &g1 : group_users_data)
	{
		auto ud = g1.second;
		sort(ud.begin(), ud.end());
	}

	for (auto &g1 : group_users_data)
	{
		for (auto &g2 : group_users_data)
		{
			if (g1 <= g2)
			{
				auto u1 = g1.second;
				auto u2 = g2.second;

				set<unsigned long> inter_set;
				set_intersection(
					u1.begin(), u1.end(),
					u2.begin(), u2.end(),
					inserter(inter_set, inter_set.begin()));
				auto inter_len = inter_set.size();

				if (inter_len > 0)
					fprintf(file, "%lu,%lu,%zu", g1.first, g2.first, inter_len);

				printf("Handled %lu - %lu\n", g1.first, g2.first);
			}
		}
	}
	fclose(file);
}

int main(int argc, char *argv[])
{
	if (argc != 3)
	{
		printf("Specify i/o files!");
		return 1;
	}

	auto input_filename = argv[1];
	auto output_filename = argv[2];

	auto group_users_data = load_group_users(input_filename);
	calc_and_write_group_shr(group_users_data, output_filename);


	return 0;
}