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 ;
 }