POJ 1611 The Suspects （并查集）

The Suspects

Time Limit: 1000MS Memory Limit: 20000K
Total Submissions: 33167 Accepted: 16083

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：有一个感染体为0，然后给你几个集合，问最后有多少嫌疑人

思路：按照普通的并查集，只不过以0为根，最后查询根为0的结点个数就行了

ac代码：

/* ***********************************************Author       : AnICoo1Created Time : 2016-07-31-15.29 SundayFile Name    : D:\MyCode\2016-7月\2016-7-31.cppLANGUAGE     : C++Copyright  2016 clh All Rights Reserved************************************************ */#include<stdio.h>#include<math.h>#include<string.h>#include<stack>#include<set>#include<map>#include<queue>#include<vector>#include<iostream>#include<algorithm>#define MAXN 1010000#define LL long long#define ll __int64#define INF 0xfffffff#define mem(x) memset(x,0,sizeof(x))#define PI acos(-1)#define eps 1e-8using namespace std;ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}ll lcm(ll a,ll b){return a/gcd(a,b)*b;}ll powmod(ll a,ll b,ll MOD){ll ans=1;while(b){if(b%2)ans=ans*a%MOD;a=a*a%MOD;b/=2;}return ans;}double dpow(double a,ll b){double ans=1.0;while(b){if(b%2)ans=ans*a;a=a*a;b/=2;}return ans;}//headint fa[MAXN];int findroot(int x){    int r=x;    while(r!=fa[r]) r=fa[r];    int i=x,j;    while(i!=r) j=fa[i],fa[i]=r,i=j;    return r;}int main(){    int n,m;    while(scanf("%d%d",&n,&m)!=EOF,n||m)    {        for(int i=0;i<n;i++) fa[i]=i;        for(int i=0;i<m;i++)        {            int a,last,c;scanf("%d",&a);            if(a) scanf("%d",&last);            for(int j=1;j<a;j++)            {                scanf("%d",&c);                int nx=findroot(c);                int ny=findroot(last);                if(nx!=ny)                {                    if(ny==0)                        fa[nx]=ny;                    else                        fa[ny]=nx;                }            }        }        int ans=0;        for(int i=0;i<n;i++)            if(findroot(i)==0)            ans++;        printf("%d\n",ans);    }    return 0;}