poj 1011 搜索减枝

题目链接：http://poj.org/problem?id=1011

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

const int maxn = 100;

int a[maxn];
int N;
int sum;
int len,cnt;
bool used[maxn];

bool cmp(int a,int b){
    return a > b;
}
bool dfs(int u,int curlen,int num){
    if(num == cnt)  return true;

    for(int i=u;i<=N;i++){
        if(used[i]) continue;
        if(!used[i-1] && a[i-1] == a[i])  continue;  

        if(curlen + a[i] == len){
            used[i] = true;
            if(dfs(num+2,0,num+1))  return true;
            used[i] = false;
            return false;
        }
        else if(curlen + a[i] < len){
            used[i] = true;
            if(dfs(i+1,curlen+a[i],num))  return true;
            used[i] = false;
            if(curlen == 0)  return false;  //一个大的都不能够找到答案，一个小的就更不可能了。
        }
    }
    return false;
}
int main()
{
 // freopen("E:\acm\input.txt","r",stdin);
    while(cin>>N && N){
        sum = 0;
        for(int i=1;i<=N;i++){
            scanf("%d",&a[i]);
            sum += a[i];
        }
        sort(a+1,a+N+1,cmp);
        a[0] = -1;
        for(len=a[1];len<sum;len++){
            if(sum % len) continue;
            cnt = sum / len;
            memset(used,0,sizeof(used));

            if(dfs(1,0,0)) break;
        }
        printf("%d
",len);
    }
}