Theft of Blueprints

#include <iostream>
#include <vector>
#include <cstdio>
#include <cmath>
using namespace std;

const int MAXN = 2000;
__int64 c[MAXN][MAXN];

int main()
{
    int n, k, temp;
    scanf("%d %d", &n, &k);
    for (int i = 0; i < n - 1; ++i)
    {
        c[i][i] = -1;
        for (int j = i + 1; j < n; ++j)
        {
            scanf("%d", &temp);
            c[j][i] = c[i][j] = temp;
        }
    }
    c[n - 1][n - 1] = -1;
    __int64 sum = 0, cnt = 0;
    if (k == 1 || (k > 2 && n == k + 1))
    {
        cnt = n;
        for (int i = 0; i < n; ++i)
            for (int j = 0; j < n; ++j)
                if (c[i][j] != -1)
                    sum += c[i][j];
    }
    if (k == 2)
    {
        cnt = n * (n - 1) / 2;
        vector<int> vect;
        for (int i = 0; i < n; ++i)
        {
            vect.clear();
            for (int j = 0; j < n; ++j)
                if (c[i][j] != -1)
                    vect.push_back(j);
            for (int j = 0; j < vect.size(); ++j)
                for (int z = j + 1; z < vect.size(); ++z)
                    sum += c[i][vect[j]] + c[i][vect[z]];
        }
    }
    cout << sum / cnt << endl;
    return 0;
}