POJ 1611 The Suspects（并查集）

The Suspects

Time Limit: 1000MS

Memory Limit: 20000K

Total Submissions: 28347

Accepted: 13820

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 42 1 25 10 13 11 12 142 0 12 99 2200 21 55 1 2 3 4 51 00 0

Sample Output

411

题意：为了预防非典，要对嫌疑患者进行隔离。规定编号为0的同学为嫌疑患者。每个嫌疑患者的同组同学都是嫌疑

患者。编写程序，找出嫌疑患者的个数。

题解：很裸的并查集问题，将每一组同学的根节点合并，最后找出和0根节点相等的个数即可。

代码如下：

#include<cstdio>#include<cstring>#define max 30010int set[max],a[max];int find(int x){int r=x;int t;while(r!=set[r])    r=set[r];    while(x!=r)    {    t=set[x];    set[x]=r;    x=t;    }    return r;}void merge(int a,int b){int fa=find(a);int fb=find(b);if(fa!=fb)   set[fa]=fb;}int main(){int n,m,k,i;while(scanf("%d%d",&n,&m)&&n||m){for(i=0;i<n;++i)   set[i]=i;    while(m--)    {    scanf("%d",&k);    for(i=0;i<k;++i)       scanf("%d",&a[i]);    for(i=0;i<k-1;++i)       merge(a[i],a[i+1]);    }int count=0;for(i=0;i<n;++i){if(find(i)==find(0))//查找根节点    count++;}printf("%d\n",count);}return 0;}