poj 1011 dfs+剪枝

据说是剪枝神题，剪枝确实是挺多的，少一个有可能都会超时。

#include <algorithm>
#include <cstring>
#include <cstdio>
using namespace std;

const int N = 100;
int stick[N];
bool used[N];
int n, snum, slen;

bool dfs( int num, int len, int pos )
{
    if ( num == snum ) return true;
    for ( int i = pos; i < n; i++ )
    {
        if ( !used[i] )
        {
            int tmp = stick[i] + len;
            if ( tmp > slen ) continue;
            used[i] = 1;
            if ( tmp == slen )
            {
                if ( dfs( num + 1, 0, 0 ) ) return true;
                used[i] = 0;
                return false;
            }
            else
            {
                if ( dfs( num, tmp, i + 1 ) ) return true;
                used[i] = 0;
            }
            if ( len == 0 ) return false;
            while ( stick[i] == stick[i + 1] ) i++;
        }
    }
    return false;
}

bool cmp( int a, int b )
{
    return a > b;
}

int main ()
{
    while ( scanf("%d", &n), n )
    {
        int sum = 0;
        for ( int i = 0; i < n; i++ )
        {
            scanf("%d", stick + i);
            sum += stick[i];
        }
        sort( stick, stick + n, cmp );
        stick[n] = -1;
        int maxn = stick[0];
        for ( int i = maxn; i <= sum; i++ )
        {
            if ( sum % i == 0 )
            {
                snum = sum / i;
                slen = i;
                memset( used, 0, sizeof(used) );
                if ( dfs( 0, 0, 0 ) )
                {
                    printf("%d
", i);
                    break;
                }
            }
        }
    }
    return 0;
}