hdu 2068

ps:长度长到我不想说....WA了无数次...25的阶乘就爆炸...

代码:

#include "stdio.h"
#define LL long long
LL fac(long long a);
LL dp[25];
LL fac1(LL a,LL b);
int main(){
    LL i,n,s;
    LL k,sum;
    dp[0]=0;
    dp[1]=1;
    for(i=2;i<20;i++)
        dp[i]=i*(dp[i-2]+dp[i-1]);

    while(~scanf("%I64d",&n) && n){
        sum=0;
        k=n/2;
        if(n%2==1) k++;
        while(n-k>=2){
            sum+=fac1(n,n-k)*dp[n-k-1];
            k++;
        }
        printf("%I64d\n",sum+1);
    }
    return 0;
}
LL fac(long long a){
    int i;
    LL sum=1;
    for(i=1;i<=a;i++){
        sum*=i;
    }
    return sum;
}
LL fac1(LL a,LL b){
    long long i,k,t,sum,sum1;
    k=a-b;
    if(k>b){
        t=k;
        k=b;
        b=t;
    }
    sum=1;
    for(i=a;i>b;i--){
        sum*=i;
    }
    sum1=fac(k);
    return sum/sum1;
}