Submission #1993792

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Source Code Expand

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<cstdlib>
using namespace std;

const int N=5005;
const int mod=1000000007;

int n,ans;
int dp[2][N][N],d[N],fac[N],inv[N];

int quickpow(int x,int y){
	int s=1;
	for (;y;y>>=1,x=1ll*x*x%mod)
		if (y&1) s=1ll*s*x%mod;
	return s;
}

void init(){
	int i;
	fac[0]=inv[0]=1;
	for (i=1;i<=n;i++) fac[i]=1ll*fac[i-1]*i%mod;
	inv[n]=quickpow(fac[n],mod-2);
	for (i=n-1;i;i--) inv[i]=1ll*inv[i+1]*(i+1)%mod;
}

int main(){
	int i,j,k,now,pre,i2;
	scanf("%d",&n);
	for (i=1;i<=n;i++) scanf("%d",&d[i]);
	init();
	dp[0][0][0]=1; now=0; pre=1;
	for (i=1;i<=n;i++){
		now^=1; pre^=1;
		for (j=0;j<=n+n;j++)
			for (k=0;k<i;k++){
				if (!dp[pre][j][k]) continue;
				(dp[now][j][k]+=1ll*dp[pre][j][k]*inv[d[i]-1]%mod)%=mod;
				if (d[i]>1&&j+d[i]-2<=n+n)
				(dp[now][j+d[i]-2][k+1]+=1ll*dp[pre][j][k]*inv[d[i]-2]%mod)%=mod;
			}
		memset(dp[pre],0,sizeof(dp[pre]));
	}
	i2=quickpow(2,mod-2);
	for (j=0;j<=n+n;j++)
		for (k=3;k<=n;k++){
			if (!dp[now][j][k]) continue;
			if (k<n&&j==0) continue;
			if (k==n&&j==0){
				(ans+=1ll*i2*dp[now][j][k]%mod*fac[k-1]%mod)%=mod;
				continue;
			}
			(ans+=1ll*i2*dp[now][j][k]%mod*fac[k-1]%mod*fac[n-k-1]%mod*j%mod)%=mod;
		}
	printf("%d\n",ans);
	return 0;
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:32:16: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d",&n);
                ^
./Main.cpp:33:38: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
  for (i=1;i<=n;i++) scanf("%d",&d[i]);
                                      ^

Judge Result