Code Up 9.6问题 D: More is better（并查集的应用）

问题 D: More is better

 

题目描述

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.

输入

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)

输出

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

样例输入

3
1 3
1 5
2 5
4
3 2
3 4
1 6
2 6

样例输出

4
5

题意为求给定集合中元素个数最多是多少。并查集的应用。

这题有点坑，一定要特别注意一开始就要1000000个人！所以father和isroot数组必须整个数组初始化，查询时也要在整个数组中查询！

参考代码：

#include
const int N=10000010;
int father[N];
int isroot[N];
int findfather(int x)
{
	int a=x;
	while(x!=father[x]) //寻找根结点 
		x=father[x];
	while(a!=father[a]) //路径压缩 
	{
		int z=a;
		a=father[a];
		father[z]=x;
	}
	return x;
}
void Union(int a,int b)
{
	int fa=findfather(a);
	int fb=findfather(b);
	if(fa!=fb)
		father[fa]=fb;
}
void init()
{
	for(int i=1;i