Submission #18999

#	Time	Username	Problem	Language	Result	Execution time	Memory
18999		kriii	악수 (kriii4_D)	C++14	5 / 100	262 ms	2888 KiB

D

#include <stdio.h>

const long long mod = 1000000007;
long long inv[450],comb[450][450],end[31][450],all[31][450];

int main()
{
	int n,m; scanf ("%d",&n);
	comb[0][0] = comb[1][0] = comb[1][1] = inv[1] = 1;
	for (int i=2;i<450;i++){
		comb[i][0] = comb[i][i] = 1;
		for (int j=1;j<i;j++) comb[i][j] = (comb[i-1][j-1] + comb[i-1][j]) % mod;
		inv[i] = (mod - mod / i) * inv[mod % i] % mod;
	}

	end[1][0] = all[1][0] = 1;
	for (int v=2;v<=n;v++){
		int l = v * (v - 1) / 2;
		for (int e=v-1;e<=l;e++){
			for (int i=0;i<v-1;i++) for (int j=0;j<e;j++){
				long long add = comb[v-1][i] * comb[e-1][j] % mod;
				add = add * all[i+1][j] % mod;
				add = add * all[v-i-1][e-j-1] % mod;
				add = add * (i + 1) * (v - i - 1) % mod;
				end[v][e] += add;
			}
			end[v][e] %= mod;
			all[v][e] = (end[v][e] + (l - e + 1) * all[v][e-1]) % mod;
		}
	}

	long long coeff = 1, ans = 0;
	m = n * (n - 1) / 2;
	for (int i=1;i<=m;i++){
		coeff = coeff * inv[m-i+1] % mod;
		ans = (ans + end[n][i] * coeff % mod * i) % mod;
	}
	printf ("%lld\n",ans);

	return 0;
}

• Subtask 1: 5 / 5
• Subtask 2: 0 / 95