学步园

一个错排公式直接解决  水过

#include<stdio.h>
long long num[25];
void chart( )
{
     num[1] = 0;
     num[2] = 1;
     for( int i = 3; i < 25; ++i )
          num[i] = ( num[i-1] + num[i-2] ) * ( i - 1 );
 }
int main( )
{
    chart( );
    int n;
    while( scanf( "%d",&n ) != EOF )
           printf( "%I64d\n",num[n] );
    return 0;
}