Submission #878975

#	Time	Username	Problem	Language	Result	Execution time	Memory
878975		Youssif_Elkadi	Magneti (COCI21_magneti)	C++17	30 / 110	1078 ms	604 KiB

Main

#include <bits/stdc++.h>
using namespace std;
const long long N = 1e4 + 5, mod = 1e9 + 7;
long long fac[N], inv[N];
long long n, l;
long long fp(long long base, long long power)
{
    long long ret = 1;
    while (power)
    {
        if (power & 1)
            ret = (ret * base) % mod;
        power >>= 1;
        base = (base * base) % mod;
    }
    return ret;
}
long long ncr(long long nn, long long rr)
{
    if (rr > nn || rr < 0)
        return 0;
    return ((fac[nn] * inv[rr]) % mod * inv[nn - rr]) % mod;
}
int main()
{
    ios_base::sync_with_stdio(0), cin.tie(NULL), cout.tie(NULL);
    cin >> n >> l;
    vector<pair<int, long long>> arr(n);
    for (int i = 0; i < n; i++)
        cin >> arr[i].first, arr[i].second = i;
    fac[0] = fac[1] = 1;
    for (long long i = 2; i <= l; i++)
        fac[i] = (i * fac[i - 1]) % mod;
    inv[l] = fp(fac[l], mod - 2);
    for (long long i = l - 1; i >= 0; i--)
        inv[i] = (inv[i + 1] * (i + 1)) % mod;
    sort(arr.begin(), arr.end());
    long long ans = 0;
    if (arr[0].first == arr[n - 1].first)
    {
        int boxe = l - (1 + arr[0].first * (n - 1));
        cout << (ncr(n + boxe, boxe) * fac[n]) % mod << "\n";
        return 0;
    }
    do
    {
        int boxes = l - n;
        for (int i = 1; i < n; i++)
            boxes -= max(arr[i - 1].first - 1, arr[i].first - 1);
        ans = (ans + ncr(n + boxes, boxes)) % mod;
    } while (next_permutation(arr.begin(), arr.end()));
    cout << ans << "\n";
}

• Subtask 1: 10 / 10
• Subtask 2: 20 / 20
• Subtask 3: 0 / 30
• Subtask 4: 0 / 50