7-25 朋友圈 (25分)-并查集

//AC
#include <iostream>
#include <string>
#include <cstring>
using namespace std;
int find(int k, int r[])
{
    int root = k;
    while (root != r[root])
    {
        root = r[root];
    }
    return root;
}
int main()
{
    int c[30001] = {0};
    int r[30001] = {0};
    int flag[30001]={0};
    int n1, n2;
    cin >> n2 >> n1;
    for(int i=0;i<=n2;i++)r[i]=i;
    for (int i = 0; i < n1; i++)
    {
        int n;
        cin >> n;
        int f;
        for (int j = 0; j < n; j++)
        {
            int t;
            cin >> t;
            flag[t]=1;
            if (j == 0)
            {
                f = t;
            }
            else
            {
                r[find(t,r)] = find(f, r);
            }
        }
    }
    int max_ = 0;
    for (int i = 1; i <= n2; i++)
    {
        if(flag[i] == 1)
        {
            int t = ++c[find(i, r)];
              if (max_ < t)
            max_ = t;
        }
    }
    cout << max_ << endl;
    return 0;
}