[20250401] BOJ / G3 / 우주신과의 교감 / 신동윤

03do-new30/202504/01 BOJ G3 우주신과의 교감.md

@@ -0,0 +1,106 @@
+```java
+import java.util.*;
+import java.io.*;
+import java.awt.Point;
+public class Main {
+
+    static int N, M;
+    static Point[] points;
+    static int[] parents;
+    static PriorityQueue<Edge> pq;
+
+    static class Edge implements Comparable<Edge>{
+        int from, to;
+        double wt;
+        public Edge(int from, int to, double wt) {
+            this.from = from;
+            this.to = to;
+            this.wt = wt;
+        }
+
+        @Override
+        public int compareTo(Edge o) {
+            return Double.compare(this.wt, o.wt);
+        }
+    }
+
+    public static void main(String[] args) throws IOException {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        StringTokenizer st = new StringTokenizer(br.readLine());
+        N = Integer.parseInt(st.nextToken()); // 정점의 개수
+        M = Integer.parseInt(st.nextToken()); // 이미 연결된 통로의 개수
+
+        points = new Point[N+1];
+        for (int i = 1; i < N+1; i++) {
+            st = new StringTokenizer(br.readLine());
+            int x = Integer.parseInt(st.nextToken());
+            int y = Integer.parseInt(st.nextToken());
+            points[i] = new Point(x, y);
+        }
+
+        makeSet();
+
+        for (int i = 0; i < M; i++) {
+            // 이미 연결된 정점들에 대해 union
+            st = new StringTokenizer(br.readLine());
+            int a = Integer.parseInt(st.nextToken());
+            int b = Integer.parseInt(st.nextToken());
+            union(a, b);
+        }
+
+        makePQ();
+        double result = kruskal();
+        System.out.printf("%.2f\n", result);
+        br.close();
+    }
+
+    static double kruskal() {
+        double result = 0.0;
+        while (!pq.isEmpty()) {
+            Edge e = pq.poll();
+            if (union(e.to, e.from)) {
+                result += e.wt;
+            }
+        }
+        return result;
+    }
+
+    static void makePQ() {
+        pq = new PriorityQueue<>();
+        for (int i = 1; i < N; i++) {
+            for (int j = i+1; j < N+1; j++) {
+                pq.add(new Edge(i, j, getDist(points[i], points[j])));
+            }
+        }
+    }
+
+    static void makeSet() {
+        parents = new int[N+1];
+        for (int i = 1; i < N+1; i++) {
+            parents[i] = i;
+        }
+    }
+
+    static int find(int a) {
+        if (parents[a] == a) return a;
+        return parents[a] = find(parents[a]);
+    }
+
+    static boolean union(int a, int b) {
+        int aRoot = find(a);
+        int bRoot = find(b);
+        if (aRoot == bRoot) return false;
+        if (aRoot < bRoot) {
+            parents[bRoot] = aRoot;
+        } else {
+            parents[bRoot] = aRoot;
+        }
+        return true;
+    }
+
+    static double getDist(Point a, Point b) {
+        return Math.sqrt(Math.pow(a.x - b.x, 2) + Math.pow(a.y - b.y, 2));
+    }
+}
+
+```