> #include <iostream>
> using namespace std;
> 
> bool used[20];
> int matrix[20][20];
> int n, result;

> 
> int caculate ()
> {
> 	int sum = 0;
> 	for ( int i = 0; i < n; i++ )
> 	{
> 		if ( used[i] )
> 		{
> 			for ( int j = 0; j < n; j++ )
> 				if ( !used[j] )
> 					sum += matrix[i][j];
> 		}
> 	}
> 
> 	return sum;
> }
> 
> void search ( int index )
> {
> 	if ( index == n )
> 	{
> 		result = result > caculate () ? result : caculate ();
> 		return;
> 	}
> 
> 	used[index] = true;
> 	search ( index + 1 );
> 	used[index] = false;
> 	search ( index + 1 );
> }
> 
> int main()
> {
> 	int i, j;
> 	scanf ( "%d", &n );
> 	for ( i = 0; i < n; i++ )
> 		for ( j = 0; j < n; j++ )
> 			scanf ( "%d", &matrix[i][j] );
> 	result = -1;
> 	search ( 0 );
> 	printf ( "%d\n", result ); 
> 	return 0;
> }
> 


However, I was so close to death. For the execution time of this code is 1625MS.....ORZ...