Submission #1237516

#	Time	Username	Problem	Language	Result	Execution time	Memory
1237516		zadniprovska	Magneti (COCI21_magneti)	C++20	0 / 110	1 ms	324 KiB

Main

#include <bits/stdc++.h>

using namespace std;


#define ll long long

const ll mod = 1e9 + 7;
const ll DIM = 1e5 + 7;

ll a[DIM], fact[DIM], rfact[DIM];

ll C(ll n, ll k) {
    return (((fact[n] * rfact[k]) % mod) * rfact[n-k]) % mod;
}

ll binpow (ll a, ll p) {

    ll ans = 1;
    while (p) {
        if (p & 1) {
            ans *= a;
            ans %= mod;
        }

        a *= a;
        a %= mod;

        p >>= 1;
    }

    return ans;
}

int main(){
    ios::sync_with_stdio(false);cin.tie(nullptr); cout.tie(nullptr);
    
    ll n, L;
    cin >> n >> L;

    ll r;
    for (int i=1; i<=n; i++) {
        cin >> r;
    }

    if (n == 1) {
        cout << L << endl;
        return 0;
    }

    fact[0] = 1;
    for (int i=1; i<=n; i++) {
        fact[i] = fact[i-1] * i;
    }

    rfact[0] = 1;
    for (int i=1; i<=n; i++) {
        rfact[i] = binpow(fact[i], mod-2);
    }

    
    ll answer = 0;
    for (int i=n+(n-1)*(r-1); i<=L; i++) {


        answer += C(i - n - (n-1)*(r-1) + n-1 - 1, n-2);
        answer %= mod;

    }

    cout << (answer * fact[n]) % mod << endl;
    

}
;

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