POJ 1011 Sticks

DFS

题意是让你把这些木棍组合成长度相等的一些木棍。要求长度最短。

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
int a[65],n,sum,ans;
bool v[65],ok;
bool cmpa(int a,int b)
{
    return a>b;
}
bool dfs(int num,int need,int total)
{
    int i;
    if(need==0)
    {
        if(total==sum/ans-2)return 1;
        for(i=0;v[i];i++);
        v[i]=1;
        if(dfs(i+1,ans-a[i],total+1))return 1;
        v[i]=0;
        return 0;
    }
    else
    {
        if(num>=n-1)return 0;
        for(i=num;i<n;i++)
        {
            if(a[i]==a[i-1]&&!v[i-1])
            continue;
            if(!v[i]&&a[i]<=need)
            {
                v[i]=1;
                if(dfs(i,need-a[i],total))return 1;
                v[i]=0;
            }
        }
        return 0;
    }
}
int main()
{
    while(scanf("%d",&n),n)
    {
        sum=ans=0;
        for(int i=0;i<n;i++)
        scanf("%d",&a[i]),sum+=a[i];
        sort(a,a+n,cmpa);
        memset(v,0,sizeof(v));
        ok=0;
        for(ans=a[0];ans<=sum/2;ans++)
        {
            if(sum%ans==0)
            {
                v[0]=1;
                if(dfs(0,ans-a[0],0))
                {printf("%d
",ans);ok=1;break;}
            }
        }
        if(!ok)
        printf("%d
",sum);
    }
    return 0;
}

还有更强大的剪枝版本号的：

#include<cstdio>
#include<cstring>
#include<cstring>
#define MAX 64
int s[MAX],vis[MAX],n,len,sum;
void input()
{   int i,j,temp;
    sum = 0;
       for(i=0;i<n;i++)
         {
            scanf("%d ",&s[i]);
            sum+=s[i];
         }
      for(i=1;i<n;i++)
       for(j=0;j<n-i;j++)
       {
           if(s[j]<s[j+1])
          {
           temp = s[j];
           s[j] = s[j+1];
           s[j+1] = temp;
          }
       }
}
bool dfs(int now_len,int i,int count)
{
    if((count+1)*len==sum)
    {
        return true;
    }
    for(int k= i;k<n;k++)
    {
       if(vis[k]) continue;
       if(k&&!vis[k-1]&&s[k]==s[k-1]) continue;
       if(s[k]+now_len>len) continue;
       if(now_len+s[k]==len)
       {
           vis[k]=1;
           bool result = dfs(0,0,count+1);
           vis[k]=0; 
           return result;
       }
       else if(now_len==0)
       {
           vis[k]=1;
           bool result = dfs(s[k],k+1,count);
           vis[k]= 0;
           return result;
       }
       else if(now_len+s[k]<len)
       {
           vis[k] = 1;
           bool result = dfs(s[k]+now_len,k+1,count);
           vis[k] = 0;
           if(result)
           return true;
       }
    }
    return false;
}
int main()
{
    while(scanf("%d",&n),n)
    {
       input();
       for(len=s[0];len<=sum;len++)
       {
           if(sum%len) continue;
           memset(vis,0,sizeof(vis));
           if(dfs(0,0,0))
           break;
       }
       printf("%d
",len);
    }
}