The Suspects（POJ 1611 传染病 并查集）

The Suspects（点击转到）

Time Limit: 1000MS		Memory Limit: 20000K
Total Submissions: 50213		Accepted: 24025

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

Source

Asia Kaohsiung 2003

1.题目含义：

     n个学生分属m个团体，(0 < n <= 30000 , 0 <= m <= 500) 一个学生可以属于多个团体。一个学生疑似患病，则它所属的整个团体都疑似患病。已知0号学生疑似患病，以及每个团体都由哪些学生构成，求一共多少个学生疑似患病。

2.注意：

   2.1 并查集思路或者说模板就是：初始化——查找——合并 的过程，对应不同的题目，在后两个过程中会有相应的一些改变。

   2.2 本题就多了在合并过程中，求解总结点的过程。（因为题目中，要求一共多少个学生疑似患病）

3.代码：

#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
int n,m;
int par[30006];
int all[30006];
void init()
{
	for(int i=0;i<n;i++)
	{
		par[i]=i;
		all[i]=1;
	}
}
int getRoot(int root)
{
	if(par[root]!=root)
	    par[root]=getRoot(par[root]);
    return par[root];
}
void Merge(int x,int y)
{
	int fx=getRoot(x);
	int fy=getRoot(y);
	if(fx==fy)
	   return ;
    all[fx]=all[fx]+all[fy];
	par[fy]=fx;
}
int main()
{
	int k,first,node;
	while(cin>>n>>m){
	if(n==0&&m==0)  break;
	init();
	for(int i=0;i<m;i++)
	{
		cin>>k;
		cin>>first;
		for(int j=1;j<k;j++)
		{
			cin>>node;
			Merge(first,node);
		}
	}
	cout<<all[getRoot(0)]<<endl;
   }
	return 0;
}