1107. Social Clusters (30) -- 简单 DFS / BFS

题目地址

https://www.patest.cn/contests/pat-a-practise/1107

题目描述

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:

Ki: hi[1] hi[2] … hi[Ki]

where Ki (>0) is the number of hobbies, and hi[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

ac

这题就直接dfs，用变量标记某个人是否已经访问过

注意结果可能包含重复的
比如

4
4 3 3 1

• multiset
• 或者直接vector 然后再sort排序

ac1, DFS

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <algorithm>
#include <sstream>
#include <stack> 
#include <map> 
#include <set> 
#include <unordered_map>

using namespace std;

const int INF = 0x7fffffff;
const int MIN_INF = - INF -1;
typedef long long int LL;

const int N = 1001;

int n;

vector<int> hobbys[N];
vector<int> persons[N];

bool vis[N];

int cnt;

void dfs(int index,int depth)
{
    //cout << index << endl;
    cnt ++;

    int len = persons[index].size();

    for(int i=0;i<len;i++)
    {
        int h = persons[index][i];

        int lenh = hobbys[h].size();

        for(int j=0;j<lenh;j++)
        {
            int perh = hobbys[h][j];
            if(perh != index && !vis[perh])
            {
                vis[perh] = true;
                dfs(perh,depth + 1);
            }
        }
    }
}
int main()
{
    //freopen("in.txt","r",stdin);
    while(scanf("%d", &n) != EOF)
    {
        for(int i=0;i<N;i++)
        {
            hobbys[i].clear();
            persons[i].clear();
            vis[i] = false;
        }

        int k,h;
        for(int i=0;i<n;i++)
        {
            scanf("%d:", &k);
            for(int j = 0;j<k;j++)
            {
                scanf("%d",&h);
                persons[i+1].push_back(h);
                hobbys[h].push_back(i+1);
            }
        }

        vector<int> ans;
        for(int i=1;i<=n;i++)
        {
            if(vis[i] == false)
            {
                vis[i] = true;
                cnt = 0;
                dfs(i,1);
                ans.push_back(cnt);
            }
        }

        int len = ans.size();

        sort(ans.begin(), ans.end());

        printf("%d\n",len);
        for(int i= len-1;i>0;i--)
        {
            printf("%d ", ans[i]);
        }
        printf("%d\n", ans[0]);
    }

    //printf("\n");
    return 0;
}

ac2, BFS

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <algorithm>
#include <sstream>
#include <list>
#include <stack> 
#include <map> 
#include <set> 
#include <iterator> 
#include <unordered_map>

using namespace std;

const int INF = 0x7fffffff;

typedef long long int LL;

const int N = 1000 + 5;

int n;

vector<int> hobby[N];

vector<int> hpo[N];

bool vis[N];

int bfs(int id)
{
  int cnt = 1;

  queue<int> que;
  que.push(id);
  while(!que.empty())
  {
    int tid = que.front();
    que.pop();

    int tHobbysSize = hobby[tid].size();
    for(int i=0;i<tHobbysSize;i++)
    {
      int th = hobby[tid][i];
      int othersSize = hpo[th].size();
      for(int j = 0;j < othersSize; j ++)
      {
        int oId = hpo[th][j];
        if(vis[oId] == false)
        {
          que.push(oId);
          vis[oId] = true;
          cnt ++;
        }
      }
    }
  }

  return cnt;
}

bool cmp(int a, int b)
{
  return a > b;
}

int main()
{
  //freopen("in.txt", "r" , stdin);

  while(scanf("%d", &n) != EOF)
  {
    for(int i=1;i<=n;i++)
    {
      int k;
      scanf("%d: ", &k);
      while(k--)
      {
        int tmp;
        scanf("%d", &tmp);
        hobby[i].push_back(tmp);
        hpo[tmp].push_back(i);
      }
    }

    for(int i=1;i<=n;i++)
    {
      vis[i] = false;
    }

    vector<int> ans;
    int ansLen = 0;

    for(int i=1;i<=n;i++)
    {
      if(vis[i] == false)
      {
        vis[i] = true;
        int cnt = bfs(i);
        ans.push_back(cnt);
        ansLen ++;
      }
    }
    if(ansLen > 1)
      sort(ans.begin(), ans.end(), cmp);

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

    printf("%d", ans[0]);
    for(int i=1;i<ansLen;i++)
    {
      printf(" %d", ans[i]);
    }
    printf("\n");
  }
  return 0;
}