HDU_1455_dfs

http://acm.hdu.edu.cn/showproblem.php?pid=1455

 

int dfs(int all,int sum,int now)，all代表剩余总长，sum，代表每段长，now代表当前拼接的长度。

if(a[i]+now == sum || now == 0) return 0;
while(a[i+1] == a[i]) i++;

这两句话剪枝很重要。

 

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

int a[55],used[55],n;

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

int dfs(int all,int sum,int now)
{
    if(all == 0 && now == sum)  return 1;
    if(now == sum)  now = 0;
    for(int i = 1;i <= n;i++)
    {
        if(used[i] || a[i]+now > sum)   continue;
        used[i] = 1;
        if(dfs(all-a[i],sum,now+a[i]))  return 1;
        used[i] = 0;
        if(a[i]+now == sum || now == 0) return 0;
        while(a[i+1] == a[i])   i++;
    }
    return 0;
}
int main()
{
    while(cin >> n && n)
    {
        int sum = 0;
        for(int i = 1;i <= n;i++)
        {
            cin >> a[i];
            sum += a[i];
        }
        sort(a+1,a+n+1,cmp);
        for(int i = a[1];i <= sum;i++)
        {
            if(sum%i)   continue;
            memset(used,0,sizeof(used));
            if(dfs(sum,i,0))
            {
                cout << i << endl;
                break;
            }
        }
    }
    return 0;
}