杭电 1856 并查集路径压缩+按秩合并

          这道题是下午看的，当时看了不会，后来看算法导论上有，有看了一些其他的资料，就做出来了。不过杭电数据坑爹啊，，，竟然有n=0的情况，让我wr了好几次。。。。题目：

More is better

Time Limit: 5000/1000 MS (Java/Others)    Memory Limit: 327680/102400 K (Java/Others)
Total Submission(s): 4078    Accepted Submission(s): 1511

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.
 

ac代码：

#include <iostream>
#include <cstdio>
#include <string.h>
using namespace std;
const int N=10000005;
int maxx,father[N],rankk[N];
void init(int x){
  for(int i=0;i<N;++i)
  {father[i]=i;rankk[i]=1;}
}
int find(int x){
  if(father[x]!=x)
	  father[x]=find(father[x]);
  return father[x];
}
void unionset(int a,int b){
  int x=find(a);
  int y=find(b);
 
  if(x==y)
	  return;
  if(rankk[x]>=rankk[y]){
    father[y]=x;
	rankk[x]+=rankk[y];
	if(rankk[x]>maxx)
		maxx=rankk[x];
	
  }
  else{
    father[x]=y;
	rankk[y]+=rankk[x];
	if(rankk[y]>maxx)
		maxx=rankk[y];
	
  }
}
int main(){
  int n;
  while(scanf("%d",&n)!=EOF){
	  if(n==0)
	  { printf("1\n");continue;}
    init(n);
	maxx=0;
	int a,b;
	while(n--){
	  scanf("%d%d",&a,&b);
	  unionset(a,b);
	}
	printf("%d\n",maxx);
  }
  return 0;
}