Facebook Hacker Cup Rount1 #1 CardGame

CardGame.cpp

#include <cstdio>
#include <iostream>
#include <vector>
#include <map>

using namespace std;
#define MODULO 1000000007

long factorial(long k)
{
    if(k == 1 || k == 0)
    {
        return 1;
    }else{
        return (k * factorial(k - 1)) % MODULO;
    }
}


long solve(vector<long> data, long N, long K)
{
    vector<long>::iterator it;
    long result = 0;
    long fact_k = factorial(K-1);
    long fact_n = fact_k;
    long fact_n_k = 1;
    long count = 1;
    for(it = data.begin() + K - 1; it != data.end(); ++it)
    {
        result += (*it) * fact_n / fact_k / fact_n_k; result %= MODULO;
        fact_n_k *= count; fact_n_k %= MODULO;
        fact_n *= (count + K-1); fact_n %= MODULO;
        ++count;
    }
    return result;
}

int main()
{
    int T;
    long N, K;
    scanf("%d", &T);
    long chunk;
    vector<long> data;
    vector<long>::iterator it;
    for(int i = 0; i < T; ++i)
    {
        scanf("%ld %ld", &N, &K);
        for(long j = 0; j < N; ++j){
            cin >> chunk;
            data.push_back(chunk);
        }
        sort(data.begin(), data.end());
        printf("Case #%d: %ld\n", i+1, solve(data, N, K));
        data.clear();
    }
}