并查集算法 — 从大数据开发入门到夺门面出！

#include <iostream>
#include <vector>
#include <unordered_map>
#include <unordered_set>
#include <numeric>
#include <algorithm>

using namespace std;
const int N = 1E4;

int n;
vector<int> p(N);
unordered_set<int> ids;

int Find(int x) {
  return p[x] ^ x ? p[x] = Find(p[x]) : x;
}

void Union(const int u, const int v) {
  p[Find(u)] = p[Find(v)];
}

int main(void) {
  // initialize
  iota(begin(p), end(p), 0);

  scanf("%d", &n);
  unordered_map<int, pair<int, int>> infos;
  for (int i = 0; i < n; ++i) {
    int id, father, mother, k;
    scanf("%d %d %d %d", &id, &father, &mother, &k);
    ids.emplace(id);
    if (father != -1) Union(id, father), ids.emplace(father);
    if (mother != -1) Union(id, mother), ids.emplace(mother);
    while (k--) {
      int child;
      scanf("%d", &child);
      Union(child, id);
      ids.emplace(child);
    }
    int estate, area;
    scanf("%d %d", &estate, &area);
    infos[id] = { estate, area };
  }

  // statistics 统计信息
  unordered_map<int, vector<int>> statistics;
  for (const auto& id : ids)
    statistics[Find(id)].emplace_back(id);

  vector<vector<double>> ans;
  for (auto&& [_, members] : statistics) {
    int total_estate = 0, total_area = 0;
    for (const int member : members) {
      total_estate += infos[member].first;
      total_area += infos[member].second;
    }
    ans.push_back({
        *min_element(begin(members), end(members)),
        members.size(),
        static_cast<double>(total_estate) / members.size(), 
        static_cast<double>(total_area) / members.size()}
    );
  }

  // 按人均房产面积降序顺序输出所有家庭信息。
  sort(begin(ans), end(ans), [](const auto& a, const auto& b) {
    return a[3] > b[3];
  });

  printf("%d\n", ans.size());
  for (const auto& v : ans)
    printf("%04d %d %.3f %.3f\n", static_cast<int>(v[0]), static_cast<int>(v[1]), v[2], v[3]);

}