链接：https://pintia.cn/problem-sets/994805046380707840/problems/994805068539215872

题解：很简单的并查集，这可能是我在PTA上写过的最长的代码了

代码：

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int M = int(1e5);
struct p
{
    int ind;
    int fa, ma;
    int cnt;
    int area;
    int peo;
    double Area;
    p()
    {
        cnt = area = Area = 0;
        fa = peo = 0;
    }
    //int f;
}a[M],ans[M];
int root[M];
void init()
{
    for (int i = 0; i <= M; i++)
        root[i] = i;
}
int Find(int x)
{
    int r = x;
    while (root[r] != r)
        r = root[r];
    int i;
    while (x != r)
    {
        i = root[x];
        root[x] = r;
        x = i;
    }
    return r;

}
void join(int x, int y)
{
    int fx = Find(x);
    int fy = Find(y);
    if (fx > fy)root[fx] = fy;
    else root[fy] = fx;
}

bool cmp(p a, p b)
{
    if (a.Area == b.Area)
        return a.ind < b.ind;
    else
        return a.Area > b.Area;
}
int k, x,sum;
int main()
{
    init();
    int n; cin >> n;
    for (int i = 0; i < n; i++)
    {
        cin >> a[i].ind >> a[i].fa >> a[i].ma>>k;
        if (a[i].fa != -1) 
            join(a[i].ind, a[i].fa);
        if (a[i].ma != -1)
            join(a[i].ind, a[i].ma);
        for (int j = 0; j < k; j++)
        {
            cin >> x;
            join(a[i].ind, x);
        }
        cin >> a[i].cnt >> a[i].area;
    }
    for (int i = 0; i < n; i++)
    {
        int r = Find(a[i].ind);
        ans[r].ind = r;
        ans[r].area += a[i].area;
        ans[r].cnt += a[i].cnt;
        ans[r].fa = -1;//?
    }
    for (int i = 0; i < M; i++)
    {
        ans[Find(i)].peo++;
        if (ans[i].fa == -1) sum++;
    }
    for (int i = 0; i < M; i++)
    {
        if (ans[i].fa == -1)
            ans[i].Area = (double)ans[i].area / ans[i].peo;
    }
    cout << sum << endl;
    sort(ans, ans + M, cmp);
    for (int i = 0; i < sum; i++)
    {
        printf("%.4d %d %.3lf %.3lf\n", ans[i].ind, ans[i].peo, (double)ans[i].cnt / ans[i].peo, ans[i].Area);
    }
    return 0;
}