HackerRank - "The Coin Change Problem"

#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
using namespace std;

typedef unsigned long long ULL;

int main()
{
    unsigned n, m;
    cin >> n >> m;
    vector<ULL> v(m);
    for (unsigned i = 0; i < m; i++)
        cin >> v[i];
    std::sort(v.begin(), v.end());

    //    dp[val][ending coin]
    vector<vector<ULL>> dp(n + 1, vector<ULL>(m, 0));
    dp[0][0] = 1;
    for (unsigned i = 0; i <= n; i++)
    for (unsigned j = 0; j < m; j ++)
    {
        for (unsigned k = j; k < m; k ++)
        {    
            if((ULL(i) + v[k]) <= ULL(n))
                dp[ULL(i) + v[k]][k] += dp[i][j];
        }
    }
    ULL ret = 0;
    for(unsigned i = 0; i < m; i ++)    ret += dp[n][i];
    cout << ret << endl;
    return 0;
}