ACM PKU 1009 http://acm.pku.cn/JudgeOnline/problem?id=1009

#include <stdio.h>

#include <stdlib.h>

int stick[64];

int used[64];

int n, m, len;

void init ( int n )
{

    for ( int i=1; i<n; i++ )
    {
        used[i] = 0;
    }
    used[0] = 1;
}

int cmp ( const void *a, const void *b )
{

    return *( int * )b - *( int * )a;
}

int dfs ( int start, int no, int cur, int last )
{

    int i, j;

    if ( ! last )
    {
        if ( cur == len )
        {
            return 1;
        }
        return 0;
    }

    if ( cur == len )
    {
        if ( m - no > last )
        {
            return 0;
        }

        for ( i=1; i<n; i++ )
        {
            if ( ! used[i] )
            {
                break;
            }
        }
        used[i] = 1;
        if ( dfs ( i+1, no+1, stick[i], last-1 ) )
        {
            return 1;
        }
        used[i] = 0;
        return 0;
    }
    else
    {
        if ( m - no > last - 1 )
        {
            return 0;
        }
        
        for ( i=start; i<n; i++ )
        {
            if ( ! used[i] && cur+stick[i] <= len )
            {
                used[i] = 1;
                if ( dfs ( i+1, no, cur+stick[i], last-1 ) )
                {
                    return 1;
                }
                used[i] = 0;

                for ( j=i+1; j<n; j++ )
                {
                    if ( stick[i] != stick[j] )
                    {
                        break;
                    }
                }
                i = j - 1;
            }
        }
        return 0;
    }
}

int main ()
{

    int t, max, sum;

    while ( scanf ( "%d", &t ) != EOF )
    {
        while ( t -- )
        {
            scanf ( "%d", &n );
            sum = 0;
            max = -1;
            for ( int i=0; i<n; i++ )
            {
                scanf ( "%d", &stick[i] );
                sum += stick[i];
                if ( max < stick[i] )
                {
                    max = stick[i];
                }
            }

            m = 4;
            if ( sum % m )
            {
                printf ( "no\n" );
            }
            else
            {
                if ( sum / m < max )
                {
                    printf ( "no\n" );
                }
                else
                {
                    init ( n );
                    len = sum / m;
                    if ( dfs ( 1, 1, stick[0], n-1 ) )
                    {
                        printf ( "yes\n" );
                    }
                    else
                    {
                        printf ( "no\n" );
                    }
                }
            }
        }
    }
    return 0;
}