BZOJ 4665

orz gery

一发rk1真有趣(其实我没想着常数优化

inline int sqr(int x){return 1ll*x*x%mo;}
const int N=2011;
int n,a[N],m;
int f[N][N];
int fac[N],fai[N];
void Init(){
	fac[0]=1;
	For(i,1,N)fac[i]=1ll*fac[i-1]*i%mo;
	fai[N-1]=Pow(fac[N-1],mo-2);
	per(i,1,N-1)fai[i-1]=1ll*fai[i]*i%mo;
}
int main(){
#ifdef flukehn
	freopen(".in","r",stdin);
#endif
	Init();
	in,n;
	rep(i,1,n){
		int x=in;
		++a[x];
		upmx(m,x);
	}
	int tot=0;
	f[0][0]=1;
	rep(i,1,m){
		rep(j,0,a[i]){
			int tmp=1ll*sqr(fac[a[i]])*sqr(fai[a[i]-j])%mo*fai[j]%mo;
			rep(k,0,tot){
				int res=1ll*f[i-1][k]*tmp%mo;
				admo(f[i][k+j],res);
			}
		}
		tot+=a[i];
	}
	ll ans=0,t=1;
	rep(i,0,n){
		ans+=t*f[m][i]*fac[n-i]%mo;
		t*=-1;
	}
	ans=(ans%mo+mo)%mo;
	rep(i,1,n)ans=1ll*ans*fai[a[i]]%mo;
	out,ans;
}