poj 1611 The Suspects 初级->数据结构->简单并查集的应用

                                                                        
The Suspects

Time Limit: 1000MS		Memory Limit: 20000K
Total Submissions: 16512		Accepted: 7923

Description
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

// 题意：简单的并查集应用。一开始0号学生是SARS，给出每个小组的人数

和每个人的编号。 并查集完事后，统计一下和0号学生在同一棵树上的人数

，即为结果。

#include<iostream>
#include<cstdio>
using namespace std;
int p[30001];
int find(int x)
{
int r=x,t;
while(x!=p[x])
x=p[x];
while(r!=x)
{
t=p[r];
p[r]=x;
r=t;
}
return x;
}
void mer(int x,int y)
{
x=find(x);
y=find(y);
if(x!=y)
p[x]=y;
}
int main()
{
int i,j;
int n,m,k,a,b,sum;
while(scanf("%d%d",&n,&m),n+m)
{
for(i=0;i<n;i++)
p[i]=i;
for(i=1;i<=m;i++)
{
cin>>k;
cin>>a;
for(j=2;j<=k;j++)
{
cin>>b;
mer(a,b);
}
}
sum=1;
for(i=1;i<n;i++)
if(find(0)==find(i))
sum++;
cout<<sum<<endl;
}
return 0;
}