[Graph] baekjoon-17472

Author: Seogeurim

README.md

@@ -269,6 +269,7 @@
 | 05  |     | [Baekjoon-1944 복제 로봇](./src/Graph/P1944)           |         |
 | 06  |     | [Baekjoon-1197 최소 스패닝 트리](./src/Graph/P1197)      |         |
 | 07  |     | [SWEA-1251 하나로](./src/Graph/swea1251)               |  Prim   |
+| 08  |     | [Baekjoon-17472 다리 만들기 2](./src/Graph/P17472)      | 삼성 A형 기출 |
 
 ### 최단 경로
 

src/Graph/P17472/Main.java

@@ -0,0 +1,122 @@
+package Graph.P17472;
+
+import java.io.*;
+import java.util.*;
+
+public class Main {
+
+    static int N, M;
+    static int[][] map;
+    static int[] di = {-1, 0, 1, 0}, dj = {0, 1, 0, -1};
+    static int[] root;
+    static PriorityQueue<Edge> pq = new PriorityQueue<>(((o1, o2) -> o1.dist - o2.dist));
+
+    public static void main(String[] args) throws Exception {
+        System.setIn(new FileInputStream("src/Graph/P17472/input.txt"));
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        StringTokenizer st = new StringTokenizer(br.readLine());
+
+        N = Integer.parseInt(st.nextToken());
+        M = Integer.parseInt(st.nextToken());
+
+        map = new int[N][M];
+        for (int i = 0; i < N; i++) {
+            st = new StringTokenizer(br.readLine());
+            for (int j = 0; j < M; j++) map[i][j] = Integer.parseInt(st.nextToken());
+        }
+
+        int iNum = 2;
+        ArrayList<Node> islands = new ArrayList<>();
+        for (int i = 0; i < N; i++) {
+            for (int j = 0; j < M; j++) {
+                if (map[i][j] == 1) island_bfs(i, j, iNum++);
+                if (map[i][j] > 0) islands.add(new Node(i, j));
+            }
+        }
+
+        for (Node p : islands) {
+            for (int k = 0; k < 4; k++) {
+                find_edge(p.i, p.j, k, map[p.i][p.j]);
+            }
+        }
+
+        root = new int[iNum];
+        for (int i = 0; i < iNum; i++) root[i] = i;
+
+        int cnt = iNum-3, ans = 0;
+        while (!pq.isEmpty() && cnt > 0) {
+            Edge e = pq.poll();
+            if (find(e.from) == find(e.to)) continue;
+            union(e.from, e.to);
+            ans += e.dist;
+            cnt --;
+        }
+
+        if (cnt > 0) System.out.println(-1);
+        else System.out.println(ans);
+    }
+
+    static int find(int n) {
+        if (root[n] == n) return n;
+        return root[n] = find(root[n]);
+    }
+
+    static void union(int a, int b) {
+        root[find(a)] = find(b);
+    }
+
+    static void find_edge(int i, int j, int d, int num) {
+        int dist = 0;
+        int ni = i + di[d], nj = j + dj[d];
+        while (isValidPath(ni, nj) && map[ni][nj] != num) {
+            if (map[ni][nj] > 0) {
+                if (dist >= 2) pq.offer(new Edge(num, map[ni][nj], dist));
+                break;
+            }
+            ni += di[d];
+            nj += dj[d];
+            dist ++;
+        }
+    }
+
+    static void island_bfs(int i, int j, int iNum) {
+        Queue<Node> q = new LinkedList<>();
+        q.offer(new Node(i, j));
+        map[i][j] = iNum;
+        while (!q.isEmpty()) {
+            Node p = q.poll();
+            for (int k = 0; k < 4; k++) {
+                int ni = p.i + di[k];
+                int nj = p.j + dj[k];
+
+                if (isValidPath(ni, nj) && map[ni][nj] == 1) {
+                    map[ni][nj] = iNum;
+                    q.offer(new Node(ni, nj));
+                }
+            }
+        }
+    }
+
+    static boolean isValidPath(int i, int j) {
+        return 0 <= i && i < N && 0 <= j && j < M;
+    }
+
+    static class Node {
+        int i, j;
+
+        public Node(int i, int j) {
+            this.i = i;
+            this.j = j;
+        }
+    }
+
+    static class Edge {
+        int from, to, dist;
+
+        public Edge(int from, int to, int dist) {
+            this.from = from;
+            this.to = to;
+            this.dist = dist;
+        }
+    }
+}

src/Graph/P17472/README.md

@@ -0,0 +1,9 @@
+## [baekjoon-17472] 다리 만들기 2
+
+![image](https://user-images.githubusercontent.com/22045163/112599943-e6c48280-8e53-11eb-8f75-c0d960743444.png)
+![image](https://user-images.githubusercontent.com/22045163/112600020-fd6ad980-8e53-11eb-9f63-faaf4aa1f03f.png)
+![image](https://user-images.githubusercontent.com/22045163/112600060-09ef3200-8e54-11eb-8cd6-c11b5e187e51.png)
+
+이 문제는 BFS + MST !!
+
+![image](https://user-images.githubusercontent.com/22045163/112600101-183d4e00-8e54-11eb-9f41-90d909a88510.png)

src/Graph/P17472/input.txt

@@ -0,0 +1,21 @@
+10 6
+0 0 0 1 0 0
+0 0 0 1 0 0
+0 1 0 0 0 1
+0 0 0 0 0 0
+1 1 0 1 1 0
+1 0 0 0 1 0
+1 1 0 0 1 0
+0 0 0 0 1 1
+0 0 0 0 0 0
+0 1 0 0 0 0
+ans: 13
+
+7 7
+1 1 1 0 1 1 1
+1 1 1 0 1 1 1
+1 1 1 0 1 1 1
+0 0 0 0 0 0 0
+1 1 1 0 1 1 1
+1 1 1 0 1 1 1
+1 1 1 0 1 1 1