The meaning of the question
: Now is the period of influenza outbreak, the school has n students, the student number is 0~n-1, and there are m clubs. Student No. 0 is a virus carrier. If there is a student and a virus carrier in the same club, then he will also become a virus carrier. For example, community 1 (0, 1, community 2 (1, 2, 3), then 0, 1, 2, and 3 are all virus carriers.
Given the number of students and clubs, ask how many virus carriers there are.
Idea
: It is enough to use union search to merge sets, and treat each community as a set and merge. Finally, find the root node of the set where student No. 0 is located, and then traverse all students. If it is the same as the root node of student No. 0, it means that they are in a set.
/// Carefully understand the Find() operation! !
#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include <string>
using namespace std;
int rk[30005],par[30005];
int a[30005];
int n,years;
void init()//initialization
{
for(int i=0;i<n;i++){
rk[i]=0;
par [i] = i;
}
}
int Find(int x)//Find the root node
{
while(x!=par[x])
x=by[x];
return x;
}
void unite(int x, int y)//Merge collection
{
x=Find(x);
y=Find(y);
if(x==y)
return ;
if(rk[x]<rk[y])
by[x]=y;
else{
by[y]=x;
if(rk[x]==rk[y])
rk[x]++;
}
}
intmain()
{
int m,x;
int a,b;
while(~scanf("%d%d",&n,&m)&&(n+m)){
init();
for(int i=0;i<m;i++){
scanf("%d",&x);
scanf("%d",&a);//Merge the first person of each community as the root node of the community
for(int j=1;j<x;j++){
scanf("%d",&b);
unite(a,b);
}
}
years=1;
for(int i=1;i<n;i++){//Find students who are in the same set as student No. 0
if(Find(i)==Find(0))
years++;
}
printf("%d\n",ans);
}
}