并查集：The Suspects(求与第n个人相关的人数)

Severe acute respiratory syndrome (SARS), an atypical pneumonia of unknown aetiology, was recognized as a global threat in mid-March 2003. To minimize transmission to others, the best strategy is to separate the suspects from others.
In the Not-Spreading-Your-Sickness University (NSYSU), there are many student groups. Students in the same group intercommunicate with each other frequently, and a student may join several groups. To prevent the possible transmissions of SARS, the NSYSU collects the member lists of all student groups, and makes the following rule in their standard operation procedure (SOP).
Once a member in a group is a suspect, all members in the group are suspects.
However, they find that it is not easy to identify all the suspects when a student is recognized as a suspect. Your job is to write a program which finds all the suspects.

Input

The input file contains several cases. Each test case begins with two integers n and m in a line, where n is the number of students, and m is the number of groups. You may assume that 0 < n <= 30000 and 0 <= m <= 500. Every student is numbered by a unique integer between 0 and n−1, and initially student 0 is recognized as a suspect in all the cases. This line is followed by m member lists of the groups, one line per group. Each line begins with an integer k by itself representing the number of members in the group. Following the number of members, there are k integers representing the students in this group. All the integers in a line are separated by at least one space.
A case with n = 0 and m = 0 indicates the end of the input, and need not be processed.

Output

For each case, output the number of suspects in one line.

样例：

题意：n个人，有一个人感染了SARS，那么和他同组的人都会感染SARS，已知0号已经被感染

输入：‎输入文件包含多个事例。每个测试用例以一行中的两个整数 n 和 m 开头，其中 n 是学生数，m 是组数。您可以假设 0 < n < = 30000，0 < = m < = 500。每个学生都由一个介于 0 和 n−1 之间的唯一整数编号，并且最初学生 0 在所有情况下都被视为嫌疑人。此行后跟组的 m 个成员列表，每个组一行。每行以整数 k 开头，其本身表示组中的成员数。在成员数量之后，有 k 个整数表示此组中的学生。一行中的所有整数至少用一个空格分隔。‎
‎n = 0 且 m = 0 的情况表示输入结束，无需处理。‎

输出：‎对于每个案例，在一行中输出嫌疑人的数量。‎

#include<iostream>
#include<cstdio>
using namespace std;

const int N=30010;

int n,m;
int p[N];
int size[N];

int find(int x)
{
	if(p[x]!=x)
		p[x]=find(p[x]);
	return p[x];
}

void solve()
{
	for(int i=0;i<=n;i++)
	{
		p[i]=i;
		size[i]=1;
	}
	
	for(int i=1;i<=m;i++)
	{
		int t;
		scanf("%d",&t);
		int a[t+10];
		
		for(int j=0;j<t;j++)
			scanf("%d",&a[j]);
		
		for(int j=0;j<t-1;j++)
		{
			int x=find(a[j]);
			int y=find(a[j+1]);
			
			if(x==y)
				continue;
			
			p[y]=x;
			size[x]+=size[y];
		}
	}
	
	printf("%d\n",size[find(0)]);
}

int main()
{
	while(~scanf("%d%d",&n,&m)&&(m||n))
		solve();
	
	return 0;
}