Hdu1521-permutation and combination

Exponential primary function G (x) = (1 + x/1! + (X ^ 2)/(2 !) +... + (X ^ n1)/(n1 !) ) * (1 + x/1! + (X ^ 2)/(2 !) +... + (X ^ n2)/(n2 !) * ...... * (1 + x/1! + (X ^ 2)/(2 !) +... + (X ^ nk)/(nk !) ) Convert the coefficient of x ^ m to temp/(m! ); Then, temp * (m! ) Is the coefficient of x ^ m.

#include<map>  #include<set>  #include<list>  #include<cmath>  #include<ctime>  #include<deque>  #include<stack>  #include<bitset>  #include<cstdio>  #include<vector>  #include<cstdlib>  #include<cstring>  #include<iomanip>  #include<numeric>  #include<sstream>  #include<utility>  #include<iostream>  #include<algorithm>  #include<functional>    using namespace std ;    double fac[ ] = { 1 , 1 , 2 , 6 , 24 , 120 , 720 , 5040 , 40320 , 362880 , 3628800 , 39916800 } ;    int main()  {      int n , m ;      double a[ 11 ] , b[ 11 ] , num1[ 11 ], num2[ 11 ];      while( scanf( "%d%d" , &n , &m ) != EOF )      {          for( int i = 0 ; i < n ; ++i )          {              scanf( "%lf" , &a[ i ] ) ;          }          for( int i = 0 ; i <= m ; ++i )              num1[ i ] = num2[ i ] = 0.0 ;          for( int i = 0 ; i <= a[ 0 ] ; ++i )          {              num1[ i ] = 1.0 / fac[ i ] ;          }          for( int i = 1 ; i < n ; ++i )          {              for( int j = 0 ; j <= m ; ++j )              {                  for( int k = 0 ; k <= a[ i ] && k + j <= m ; ++k )                  {                      num2[ k + j ] += ( num1[ j ] / fac[ k ] ) ;                  }              }              for( int j = 0 ; j <= m ; ++j )              {                  num1[ j ] = num2[ j ] ;                  num2[ j ] = 0 ;               }          }          printf( "%.lf\n" , num1[ m ] * fac[ m ] ) ;      }      return 0;  }