Lähetit

#include <iostream>
#include <vector>
#include <algorithm>
#include <unordered_map>

using namespace std;

#define ll long long
#define N 1000000007

int n,k;
ll d[101][101];
ll s[101][101];

int main()
{
	cin >> n >> k;
	if (k > 2*n-2) {
		cout << 0 << "\n";
		return 0;
	}
	s[0][0] = 1;
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= i; j++) {
			s[i][j] = j*s[i-1][j]+s[i-1][j-1];
		}
	}
	for (int i = 0; i <= n; i++) {
		d[i][0] = 1;
		for (int j = 1; j <= i; j++) {
			d[i][j] = d[i-1][j-1]+d[i-1][j];
		}
	}
	ll sum = 0;
	for (int i = max(0,k-n); i <= min(k,n); i++) {
		ll first = 0;
		for (int j = 0; j <= (n+1)/2; j++) {
			first += d[(n+1)/2][j]*s[j+n/2][n-i];
			first %= N;
		}
		ll second = 0;
		for (int j = 0; j <= n/2; j++) {
			second += d[n/2][j]*s[j+(n+1)/2][n-k+i];
			second %= N;
		}
		sum += (first*second)%N;
		sum %= N;
	}
	cout << sum%N << "\n";
}

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: ACCEPTED

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 2

Verdict: ACCEPTED

Test 7

Group: 2

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 3

Verdict: WRONG ANSWER

Test 12

Group: 3

Verdict: WRONG ANSWER

Test 13

Group: 3

Verdict: WRONG ANSWER

Test 14

Group: 3

Verdict: WRONG ANSWER

Test 15

Group: 3

Verdict: ACCEPTED