pat甲级 1107. Social Clusters (30)

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:

Sample Output:

3

4 3 1

分析：并查集的简单应用：解决关键是将人属于同一集合的合并起来，本题应该通过相同的爱好合并起来；

#include <cstdio>

#include <vector>

#include <algorithm>

using namespace std;

vector<int> father(), num();

int cnt;//记录集合数

//sort()从大到小排序比较函数

bool cmp(int a, int b){

    return a > b;

}

//初始化，每个人属于不同集合

void init(int n){

    for(int i = ; i <= n; i++){

        father[i] = i;

    }

}

int GetParent(int x){

    if(x == father[x])

        return x;

    father[x] = GetParent(father[x]);//路径压缩

    return father[x];

}

void merge(int x, int y){

    int fx = GetParent(x);

    int fy = GetParent(y);

    if(fx != fy){

        cnt--;//不属于同一集合，合并之后集合数减一

        father[fy] = fx;

    }

}

int main(){

    int n, k, h, i;

    int hobby[] = {};

    scanf("%d", &n);

    //调用初始化函数

    init(n);

    cnt = n;//初始化集合数为n

    //处理输入数据，合并集合

    for(i = ; i <= n; i++) {

        scanf("%d:", &k);

        for(int j = ; j < k; j++) {

            scanf("%d", &h);

            if(hobby[h] == )

                hobby[h] = i;

            merge(hobby[h], i);

        }

    }

    for(i = ; i <= n; i++)

        //这里一定要注意，要找到i所属集合的根节点，num加一，num[father[i]]++是有问题的，因为

        //这棵树深度不一定是2.。。即father[i]不一定是i所属集合的根节点

        num[GetParent(i)]++;

    printf("%d\n", cnt);

    sort(num.begin(), num.end(), cmp);

    printf("%d", num[]);

    for(i = ; i < cnt ; i++)

        printf(" %d", num[i]);

    return ;

}

巴特西

pat甲级 1107. Social Clusters (30)

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