HDOJ 1856 More is better(并查集，记录树的节点数)

More is better

Time Limit: 5000/1000 MS (Java/Others)    Memory Limit: 327680/102400 K (Java/Others)
Total Submission(s): 18606    Accepted Submission(s): 6845

Problem Description

Mr Wang wants some boys to help him with a project. Because the project is rather complex, the more boys come, the better it will be. Of course there are certain requirements.

Mr Wang selected a room big enough to hold the boys. The boy who are not been chosen has to leave the room immediately. There are 10000000 boys in the room numbered from 1 to 10000000 at the very beginning. After Mr Wang's selection any two of them who are still in this room should be friends (direct or indirect), or there is only one boy left. Given all the direct friend-pairs, you should decide the best way.

 

Input

The first line of the input contains an integer n (0 ≤ n ≤ 100 000) - the number of direct friend-pairs. The following n lines each contains a pair of numbers A and B separated by a single space that suggests A and B are direct friends. (A ≠ B, 1 ≤ A, B ≤ 10000000)

 

Output

The output in one line contains exactly one integer equals to the maximum number of boys Mr Wang may keep.

 

Sample Input

   
   
   
   

    
    
    
    4 1 2 3 4 5 6 1 6 4 1 2 3 4 5 6 7 8
   
   
   
   

 

Sample Output

   
   
   
   

    
    
    
    4 2 
    
    
    
    
 
     
 
      Hint 
     
 
     A and B are friends(direct or indirect), B and C are friends(direct or indirect), then A and C are also friends(indirect). In the first sample {1,2,5,6} is the result. In the second sample {1,2},{3,4},{5,6},{7,8} are four kinds of answers.  
    
    
    
    
     
   
   
   
   

 

 

并查集，查找节点数最多的树的节点的个数，注意当n等于0时，输出为1,这个略坑。

 

代码如下：

 

#include<cstdio>
#define max 10000010
int tree[max];
int father[max],count;

int find(int x)
{
	int r=x;
	int t;
	while(r!=tree[r])
	   r=tree[r];
	while(x!=r)//注意压缩路径，否则超时 
	{
		t=tree[x];
		tree[x]=r;
		x=t;
	}
	return r;
}

void megre(int a,int b)
{
	int fa,fb;
	fa=find(a);
	fb=find(b);
	if(fa!=fb)
	{
		tree[fa]=fb;
		father[fb]+=father[fa];//记录每棵树的节点数 
		if(father[fb]>count)
		   count=father[fb];
	}
}

int main()
{
	int n,i,a,b;
	while(scanf("%d",&n)!=EOF)
	{
		count=1;
		for(i=1;i<max;i++)
		{
			tree[i]=i;
			father[i]=1;//注意初始化 
		}
		while(n--)
		{
			scanf("%d%d",&a,&b);
			megre(a,b);
		}
		printf("%d\n",count);
	}
	return 0;
}