[并查集] POJ 1611 The Suspects

The Suspects

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

原题大意：对于两个整数N,M，N表示有N个人，M表示被分成了多少组。0号有传染病，和他一组的人都有嫌疑得传染病，对于每组数据，问有多少人有嫌疑。

解题思路：裸的并查集，可以用于练习模板。

#include<stdio.h>
#include<string.h>
int father[30050],n;
void init()
  {
  	 int i;
  	 memset(father,-1,sizeof(father));
  	 for(i=0;i<n;++i) father[i]=i;
  }
int find(int x)
  {
  	 if(x==father[x]) return (x);
  	 else father[x]=find(father[x]);
  	 return (father[x]);
  }
void merge(int x,int y)
  {
  	 if(find(x)!=find(y)) father[find(x)]=find(y);
  }
int main()
  {
  	 int m,i,qnum,x,pre,ans;
  	 while(~scanf("%d%d",&n,&m))
  	   {
  	   	  if(n==0&&m==0) break;
  	   	  init();
  	   	  while(m--)
  	   	    {
  	   	      scanf("%d",&qnum);
  	   	      scanf("%d",&pre);
  	   	      for(i=1;i<qnum;++i)
  	   	        {
  	   	          scanf("%d",&x);
  	   	          merge(x,pre);
				}
			}
		  ans=0;
		  for(i=0;i<n;++i) if(find(i)==find(0)) ++ans;
		  printf("%d\n",ans);
	   }
  	 return 0;
  }