usaco 2.1 holstein...组合的生成...

/*
    ID:chenjiong
    PROG:holstein
    LANG:C++
*/

#include <stdio.h>
#include <string.h>

int V;
int vitamin[30];
int G;
int feed[20][30];

int idx[20];
int limit[20];
int R;     
bool flag = false;

bool is_ok()
{
    int i,j;
    for ( i = 0; i < V; i++)
    {
        int sum = 0;
        for ( j = 0; j < R; j++)
            sum += feed[idx[j]][i];
        if ( sum < vitamin[i] )
            return false;
    }
    return true;
}

void print()
{
    int p;
    flag = true;
    printf("%d ",R);
    for ( p = 0; p < R - 1; p++)
        printf("%d ",idx[p] + 1);
    printf("%d\n",idx[R - 1] + 1);
}

void comb()
{
    //pick R among G feeds
    int i,j,k,p;
    for ( i = 0; i < R; i++)
    {
        idx[i] = i;
        limit[i] = i + G - R;
    }

    if ( is_ok() )
    {
        //check the first combination
        print();
        return;
    }
    
    for ( j = R - 1; j >= 0; j--)
    {
        if ( j == 0 && idx[j] == limit[j] )
        {
            //check the last combination
            if ( is_ok() )
            {
                print();
                break;
            }
        }

        if ( idx[j] < limit[j] )
        {
            idx[j]++;
            for ( k = j + 1; k < R; k++)
                idx[k] = idx[k - 1] + 1;
                
            if ( is_ok() )
            {
                print();
                break;
            }
            j = R;
        }
    }

}

int main()
{
    freopen("holstein.in","r",stdin);
    freopen("holstein.out","w",stdout);

    int i,j;
    scanf("%d",&V);
    for ( i = 0; i < V; i++)
        scanf("%d",&vitamin[i]);
    scanf("%d",&G);
    for ( i = 0; i < G; i++)
        for ( j = 0; j < V; j++)
            scanf("%d",&feed[i][j]);

    for ( i = 1; i <= G; i++)
    {
        R = i;
        comb();
        if ( flag )
            break;
    }

    return 0;
}