题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1856

More is better

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

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.
 

一定要仔细看题目啊！！！

Time Limit: 5000/1000 MS (Java/Others)    Memory Limit: 327680/102400 K (Java/Others)

时间限制虽然在1s 但是内存放的很宽啊！， 所以什么数组存不下等等的顾虑都抛开吧，大胆的开数组！

【代码】

#include <cstdio>
const int maxn= 10000000+10;
int father[maxn];
int num[maxn];
int Find(int x){
	while(x!=father[x]){ //路径压缩迭代版
		father[x]=father[father[x]];
		x=father[x];
	}
	return father[x];
}
void Union(int a,int b){ //合并
	int p=Find(a);
	int q=Find(b);
	if(p!=q){
		father[p]=q;
		num[q]+=num[p];
	}
}
int main(){
	int n;
	while(scanf("%d",&n)!=EOF){ 
		if(n==0){ //只剩下一个人的时候， pair数是0， 人数是1；
			puts("1");continue;
		}
		for(int i=1;i<=maxn;i++){
			num[i]=1;
			father[i]=i;
		}
		int a,b;
		int Max=0;
		for(int i=0;i<n;i++){
			scanf("%d%d",&a,&b);
			if(a>Max)
				Max=a;
			if(b>Max)
				Max=b;
			Union(a,b);
		}
		int max=0;
		 for(int i=1;i<=Max;i++){
			 if(num[i]>max)
				  max=num[i];
		 }
		printf("%d\n",max);
	}
	return 0;
}

hdu 1856 More is better(并查集)

原文：http://blog.csdn.net/chaiwenjun000/article/details/47405999