【PAT】A1107 Social Clusters ***

 

When register on a social network, you are always asked to specify your hobbies in order to find some potential friends with the same hobbies. A social cluster is a set of people who have some of their hobbies in common. You are supposed to find all the clusters.

Input Specification:

Each input file contains one test case. For each test case, the first line contains a positive integer N (≤1000), the total number of people in a social network. Hence the people are numbered from 1 to N. Then N lines follow, each gives the hobby list of a person in the format:

K​i​​: h​i​​[1] h​i​​[2] ... h​i​​[K​i​​]

where K​i​​ (>0) is the number of hobbies, and h​i​​[j] is the index of the j-th hobby, which is an integer in [1, 1000].

Output Specification:

For each case, print in one line the total number of clusters in the network. Then in the second line, print the numbers of people in the clusters in non-increasing order. The numbers must be separated by exactly one space, and there must be no extra space at the end of the line.

Sample Input:

8
3: 2 7 10
1: 4
2: 5 3
1: 4
1: 3
1: 4
4: 6 8 1 5
1: 4

Sample Output:

3
4 3 1

总结：并查集的套路 

代码：

#include <stdio.h>
#include <algorithm>
using namespace std;
const int N=1010;
int course[N]={0}; //喜好 
int isRoot[N]={0};  //记录每个节点是否作为某个节点的根结点 
int father[N];

void init(int n){
	for(int i=1;i<=n;i++){
		father[i]=i;  //自成节点 
		isRoot[i]=0;
	}
} 

bool cmp(int a,int b){
	return a>b;
}
int findFather(int x){
	int a=x;
	while(x!=father[x]){
		x=father[x];
	}
	
	while(a!=father[a]){  //压缩路径 
		int z=a;
		a=father[a];
		father[z]=x;
	}
	return x;
} 
void Union(int a,int b){
	int faA=findFather(a);
	int faB=findFather(b);
	if(faA!=faB){
		father[faA]=faB;
	}
} 
int main(){
	int n,total,k;
	scanf("%d",&n);
	init(n);  //初始化 
	for(int i=1;i<=n;i++){
		scanf("%d:",&total);
		for(int j=0;j<total;j++){
			scanf("%d",&k);
			if(course[k]==0){  //h没有人喜欢过 
				course[k]=i;  //根结点 
			}
			Union(i,findFather(course[k]));  //合并 *
		}
		
	}
	 
	for(int i=1;i<=n;i++){
		isRoot[findFather(i)]++;
	}
	int ans=0; //记录集合数目
	for(int i=1;i<=n;i++){
		if(isRoot[i]!=0){
			ans++;
		}
	}
	printf("%d\n",ans);
	sort(isRoot+1,isRoot+n+1,cmp); //* 
	for(int i=1;i<=ans;i++){
		printf("%d",isRoot[i]);
		if(i<ans) printf(" ");
	}
	return 0;
}