2016夏季练习

来源：UVALIVE6909

组合数学裸题

注意最后一个取模

代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
typedef long long LL;
LL n,m,p;
const LL MAXN = 1010;
const LL MOD = 1000000007;
LL fac[MAXN];
LL a[MAXN][MAXN];
void ini(){
	fac[0] = 1;
	fac[1] = 1;
	for(LL i=2;i<MAXN;i++){
		fac[i] = fac[i-1]*i%MOD;
	}
}
void init(){
	memset(a,0,sizeof(a));
	a[0][0] = 1;
	for(int i=1;i<MAXN;i++){
		a[i][0] = 1;
		for(int j=1;j<=i;j++)
			a[i][j] = (a[i-1][j-1]+a[i-1][j])%MOD;
	}
}
int main(){
	int T,nc=1;
	ini();
	init();
	scanf("%d",&T);
	while(T--){
		scanf("%lld%lld%lld",&n,&m,&p);
		LL ans = 0;
		ans = (n-p)*fac[n-2]%MOD;
		for(LL i=m+2;i<=n;i++){
			for(LL j=p+1;j<=n;j++){
				ans += (fac[n-(i-m+1)]%MOD)*(a[j-2][i-m-1]%MOD)%MOD;
			}
		}
		ans += (a[p-1][n-m]%MOD)*(fac[m-1]%MOD)%MOD;
		printf("Case #%d: %lld\n",nc++,ans%MOD);
	}
	return 0;
}