poj 1611 并查集

The Suspects

Time Limit: 1000MS		Memory Limit: 20000K
Total Submissions: 18435		Accepted: 8920

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

这是一道裸的并查集的题目，主要是用来熟悉该算法。话不多说，下面是代码：

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<iostream>
#include<cmath>
#define maxn  30050
using namespace std;

int pre[maxn];
int n,m;

void init()
{
     for(int i=0;i<n;i++)
        pre[i]=i;
}

int find(int x){
     int r=x;
      while(pre[r]!=r)
          r=pre[r];
     int i=x;
     int j;
     while(i!=r){
            j=pre[i];
            pre[i]=r;
            i=j;
     }
     return r;
}

void join(int a,int b){
    int x=find(a),y=find(b);
     if(x<y)
           pre[y]=x;
     else
           pre[x]=y;
}

int main(){
   int k,t,t1;
   while(scanf("%d%d",&n,&m)!=EOF){
            if(m==0&&n==0)
                break;
                init();
             int count=0;
       for(int i=0;i<m;i++){
            cin>>k;
            cin>>t;
            for(int j=1;j<k;j++){
                cin>>t1;
                join(t,t1);
            }
       }
       for(int i=0;i<n;i++){
           if(find(i)==0)
             count++;
       }
       printf("%d
",count);
    }
    return 0;
}