题解 | Freckles

#include <iostream>
#include <vector>
#include <cmath>
#include <algorithm>
#include <iomanip>
using namespace std;

struct Edge {
    int u, v;
    double w;
    Edge(int u, int v, double w) : u(u), v(v), w(w) {}
    bool operator<(const Edge& other) const {
        return w < other.w;
    }
};

vector<int> parent;

int find(int x) {
    return parent[x] == x ? x : parent[x] = find(parent[x]);
}

void unite(int x, int y) {
    parent[find(x)] = find(y);
}

int main() {
    int n;
    cin >> n;
    vector<pair<double, double>> points(n);
    for (int i = 0; i < n; i++) {
        cin >> points[i].first >> points[i].second;
    }

    vector<Edge> edges;
    for (int i = 0; i < n; i++) {
        for (int j = i + 1; j < n; j++) {
            double dx = points[i].first - points[j].first;
            double dy = points[i].second - points[j].second;
            double dist = sqrt(dx * dx + dy * dy);
            edges.emplace_back(i, j, dist);
        }
    }

    sort(edges.begin(), edges.end());
    parent.resize(n);
    for (int i = 0; i < n; i++) parent[i] = i;

    double total = 0.0;
    for (const Edge& e : edges) {
        if (find(e.u) != find(e.v)) {
            unite(e.u, e.v);
            total += e.w;
        }
    }

    cout << fixed << setprecision(2) << total << endl;
    return 0;
}