Merge pull request #71 from chaesc1/chaesc1

행성터널 MST - Kruskal

Author: chaesc1

junghun/week7/Day0904/BOJ행성터널/BOJ2887.java

@@ -0,0 +1,124 @@
+package week7.Day0904.BOJ행성터널;
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.StringTokenizer;
+
+public class BOJ2887 {
+    static class Planet {
+        int id;
+        int x;
+        int y;
+        int z;
+
+        public Planet(int id, int x, int y, int z) {
+            this.id = id;
+            this.x = x;
+            this.y = y;
+            this.z = z;
+        }
+    }
+
+    static class Node implements Comparable<Node> {
+        int u, v;
+        int cost;
+
+        public Node(int u, int v, int cost) {
+            // 연결된 두 행성
+            this.u = u;
+            this.v = v;
+            this.cost = cost;
+        }
+
+        @Override
+        public int compareTo(Node o) {
+            return this.cost - o.cost;
+        }
+    }
+
+    static ArrayList<Planet> planetList;
+    static ArrayList<Node> nodeList;
+    static int[] parent;
+    static int N;
+
+    public static void main(String[] args) throws Exception {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        StringTokenizer st;
+
+        N = Integer.parseInt(br.readLine());
+        planetList = new ArrayList<>();
+        nodeList = new ArrayList<>();
+
+        for (int i = 0; i < N; i++) {
+            st = new StringTokenizer(br.readLine(), " ");
+            planetList.add(new Planet(i, Integer.parseInt(st.nextToken()), Integer.parseInt(st.nextToken()), Integer.parseInt(st.nextToken())));
+        }
+
+        //  두 행성 A(xA, yA, zA)와 B(xB, yB, zB)를 터널로 연결할 때 드는 비용은 min(|xA-xB|, |yA-yB|, |zA-zB|)
+
+        // 각 좌표별로 정렬 후 인접한 행성들 사이의 비용을 계산하여 엣지 리스트에 추가
+        planetList.sort((a, b) -> a.x - b.x);
+        for (int i = 1; i < N; i++) {
+            int cost = Math.abs(planetList.get(i).x - planetList.get(i - 1).x);
+            nodeList.add(new Node(planetList.get(i - 1).id, planetList.get(i).id, cost));
+        }
+
+        planetList.sort((a, b) -> a.y - b.y);
+        for (int i = 1; i < N; i++) {
+            int cost = Math.abs(planetList.get(i).y - planetList.get(i - 1).y);
+            nodeList.add(new Node(planetList.get(i - 1).id, planetList.get(i).id, cost));
+        }
+
+        planetList.sort((a, b) -> a.z - b.z);
+        for (int i = 1; i < N; i++) {
+            int cost = Math.abs(planetList.get(i).z - planetList.get(i - 1).z);
+            nodeList.add(new Node(planetList.get(i - 1).id, planetList.get(i).id, cost));
+        }
+
+        // 크루스칼 알고리즘을 적용하기 위해 엣지 리스트를 정렬
+        Collections.sort(nodeList);
+
+        // makeSet()
+        // Union-Find 자료구조 초기화
+        parent = new int[N];
+        for (int i = 0; i < N; i++) {
+            parent[i] = i;
+        }
+        // 최소비용 조합
+        int result = 0;
+        int totalEdges = 0;
+
+        for (Node node : nodeList) {
+            // 두 행성이 서로 다른 집합에 존재한다면 합치기
+            if (find(node.u) != find(node.v)) {
+                union(node.u, node.v);
+                result += node.cost;
+                totalEdges++;
+                if (totalEdges == N - 1) {
+                    break;
+                }
+            }
+        }
+
+        System.out.println(result);
+    }
+
+    // 경로 압축 기법을 사용하여 부모노드 찾기
+    private static int find(int x) {
+        if (parent[x] == x) {
+            return x;
+        }
+        return parent[x] = find(parent[x]);
+    }
+
+    // 두 집합을 합치기
+    private static void union(int x, int y) {
+        int rootA = find(x);
+        int rootB = find(y);
+        if (rootA != rootB) {
+            parent[rootB] = rootA;
+        }
+    }
+}