답안 #21636

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
21636	2017-04-15T17:32:04 Z	gs14004	악수 (kriii4_D)	C++11	100 / 100	759 ms	2288 KB

D

#include <bits/stdc++.h>
using namespace std;
typedef long long lint;
typedef long double llf;
typedef pair<int, int> pi;
const int mod = 1e9 + 7;

lint ipow(lint x, lint p){
	lint ret = 1, piv = x % mod;
	while(p){
		if(p&1) ret *= piv;
		piv *= piv;
		ret %= mod;
		piv %= mod;
		p >>= 1;
	}
	return ret % mod;
}



lint fact[805], invf[805];
lint dp[805][41];

lint bino(int x, int y){
	return fact[x] * (invf[y] * invf[x-y] % mod) % mod;
}

int main(){
	int n;
	cin >> n;
	fact[0] = invf[0] = 1;
	for(int i=1; i<=800; i++){
		fact[i] = fact[i-1] * i % mod;
		invf[i] = ipow(fact[i], mod-2);
	}
	int s = bino(n, 2);
	dp[0][1] = 1;
	for(int i=1; i<=s; i++){
		for(int j=1; j<=n; j++){
			for(int k=0; k<i; k++){
				for(int l=1; l<j; l++){
					dp[i][j] += (dp[k][l] * dp[i-k-1][j-l] % mod) * 
						((l * (j - l) * bino(j, l) % mod) * bino(i-1, k) % mod);
					dp[i][j] %= mod;
				}
			}
			dp[i][j] *= ipow(2, mod-2);
			dp[i][j] += dp[i-1][j] * max(0ll, bino(j, 2) - (i - 1));
			dp[i][j] %= mod;
		}
	}
	lint ans = 0;
	for(int i=1; i<=s; i++){
		dp[i][n] *= invf[s] * fact[s-i] % mod;
		dp[i][n] %= mod;
	}
	for(int i=1; i<=s; i++){
		lint cur = dp[i][n] - dp[i-1][n] + mod;
		cur *= i % mod;
		cur %= mod;
		ans += cur % mod;
	}
	ans %= mod;
	cout << ans;
}

Subtask #1

5.0 / 5.0

#	결과	실행 시간	메모리	Grader output
1	Correct	0 ms	2288 KB	Output is correct
2	Correct	0 ms	2288 KB	Output is correct
3	Correct	0 ms	2288 KB	Output is correct
4	Correct	0 ms	2288 KB	Output is correct
5	Correct	0 ms	2288 KB	Output is correct

Subtask #2

95.0 / 95.0

#	결과	실행 시간	메모리	Grader output
1	Correct	0 ms	2288 KB	Output is correct
2	Correct	0 ms	2288 KB	Output is correct
3	Correct	0 ms	2288 KB	Output is correct
4	Correct	0 ms	2288 KB	Output is correct
5	Correct	0 ms	2288 KB	Output is correct
6	Correct	0 ms	2288 KB	Output is correct
7	Correct	3 ms	2288 KB	Output is correct
8	Correct	3 ms	2288 KB	Output is correct
9	Correct	6 ms	2288 KB	Output is correct
10	Correct	13 ms	2288 KB	Output is correct
11	Correct	16 ms	2288 KB	Output is correct
12	Correct	23 ms	2288 KB	Output is correct
13	Correct	33 ms	2288 KB	Output is correct
14	Correct	43 ms	2288 KB	Output is correct
15	Correct	63 ms	2288 KB	Output is correct
16	Correct	96 ms	2288 KB	Output is correct
17	Correct	106 ms	2288 KB	Output is correct
18	Correct	179 ms	2288 KB	Output is correct
19	Correct	203 ms	2288 KB	Output is correct
20	Correct	236 ms	2288 KB	Output is correct
21	Correct	333 ms	2288 KB	Output is correct
22	Correct	376 ms	2288 KB	Output is correct
23	Correct	526 ms	2288 KB	Output is correct
24	Correct	596 ms	2288 KB	Output is correct
25	Correct	759 ms	2288 KB	Output is correct