Submission #28043827

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Source Code Expand

#include <algorithm>
#include <iostream>
#include <vector>

struct UnionFind {
  std::vector<int> parent_or_size;
  int cnt;

  UnionFind(int n) : parent_or_size(n, -1), cnt(n) {}

  void unite(int x, int y) {
    x = find_root(x);
    y = find_root(y);
    if (x == y) {
      return;
    }
    if (-parent_or_size[x] < -parent_or_size[y]) {
      std::swap(x, y);
    }
    parent_or_size[x] += parent_or_size[y];
    parent_or_size[y] = x;
    cnt--;
  }
  bool is_same_root(int x, int y) { return find_root(x) == find_root(y); }
  int find_root(int x) {
    if (parent_or_size[x] < 0) {
      return x;
    }
    return parent_or_size[x] = find_root(parent_or_size[x]);
  }
  int size(int x) { return -parent_or_size[find_root(x)]; }
};

struct Edge {
  int u, v;
  long long w;
  Edge() {}
  Edge(int x, int y, long long z) : u(x), v(y), w(z) {}
};

bool comp(Edge &a, Edge &b) { return a.w < b.w; }

int main() {
  int N;
  std::cin >> N;

  std::vector<Edge> edges(N - 1);
  for (int i = 0; i < N - 1; i++) {
    int u, v, w;
    std::cin >> u >> v >> w;
    edges[i] = Edge(u - 1, v - 1, w);
  }

  std::sort(edges.begin(), edges.end(), comp);

  UnionFind uf_tree(N);

  long long ans = 0;
  for (int i = 0; i < N - 1; i++) {
    int u = edges[i].u;
    int v = edges[i].v;
    long long w = edges[i].w;
    ans += w * (long long)uf_tree.size(u) * (long long)uf_tree.size(v);
    uf_tree.unite(u, v);
  }

  std::cout << ans << "\n";

  return 0;
}

Submission Info

Judge Result