题目：

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.

Sample Input

100 4
2 1 2
5 10 13 11 12 14
2 0 1
2 99 2
200 2
1 5
5 1 2 3 4 5
1 0
0 0

Sample Output

4
1
1

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题意：

学生0都被认为是可疑者 ， 求与0在同一集合的人数（包括0）

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代码：

#include <iostream>
#include <cstdio> 
#include <algorithm>
using namespace std;
const int maxn=3e4+50;
int father[maxn],n,m,c,f,x;int find(int x){  //找根，路径压缩return x==father[x]?x:father[x]=find(father[x]);
}void Union(int a,int b) //合并
{int fa=find(a);int fb=find(b);if(fa!=fb) father[fa]=fb;
}void init() //初始化
{for(int i=0;i<n;i++)father[i]=i;
}int main()
{while(scanf("%d%d",&n,&m)==2 && n){init();while(m--){scanf("%d",&c);scanf("%d",&f); //先输入一个，方便后面合并for(int i=1;i<c;i++) //在输入剩余的，都与第一次输入的合并{scanf("%d",&x);Union(f,x);}}int cnt=1; //初始为1 (0是嫌疑犯)for(int i=1;i<n;i++) // 与0同集合都为嫌疑犯if(find(i)==find(0)) cnt++;cout<<cnt<<endl;}return 0;
}