师范大学 e: skyscrapers

 #include<iostream>

 #include<stdio.h>

 #include<cstring>

 #include<cstdlib>

 using namespace std;

 typedef __int64 LL;

 const LL mod = ;

 LL cnm[][];

 LL  dp[][];

 void prepare()

 {

     LL i,j;

     for(i=;i<=;i++)

     {

         cnm[][i]=;

         cnm[i][]=;

     }

     for(i=;i<=;i++)

     {

         for(j=;j<=i&&j<=;j++)

         {

             if(i==j) { cnm[i][j]=;continue;}

             if(j==) { cnm[i][j]=i;continue;}

             cnm[i][j]=(cnm[i-][j]+cnm[i-][j-])%mod;

         }

     }

     dp[][]=;

     for(i=;i<=;i++)

         for(j=;j<=;j++)

             dp[i][j]=(dp[i-][j-]+((i-)*dp[i-][j])%mod)%mod;

 }

 int main()

 {

     LL n,a,b,cur;

     LL l,r;

     prepare();

     while(scanf("%I64d%I64d%I64d",&n,&a,&b)>)

     {

         if(n==&&a==&&b==)break;

         l=a;r=n-b+;

         for(cur=;l<=r;l++)

         {

             cur=( cur+((cnm[n-][l-]*dp[l-][a-])%mod)*dp[n-l][b-])%mod;

         }

         printf("%I64d\n",cur);

     }

     return ;

 }