Merge pull request #1361 from AlgorithmWithGod/JHLEE325

[20251109] BOJ / G3 / 치즈 / 이준희

Author: ShinHeeEul

JHLEE325/202511/09 BOJ G3 치즈.md

@@ -0,0 +1,89 @@
+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    static int N, M;
+    static int[][] map;
+    static boolean[][] external;
+    static int[] dy = { -1, 0, 1, 0 };
+    static int[] dx = { 0, 1, 0, -1 };
+
+    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());
+        M = Integer.parseInt(st.nextToken());
+
+        map = new int[N][M];
+        int cheeseCount = 0;
+        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());
+                if (map[i][j] == 1) cheeseCount++;
+            }
+        }
+
+        int time = 0;
+        while (cheeseCount > 0) {
+            external = new boolean[N][M];
+            markExternalAir();
+
+            List<int[]> meltList = new ArrayList<>();
+            for (int i = 0; i < N; i++) {
+                for (int j = 0; j < M; j++) {
+                    if (map[i][j] == 1) {
+                        int contact = 0;
+                        for (int d = 0; d < 4; d++) {
+                            int ny = i + dy[d];
+                            int nx = j + dx[d];
+                            if (ny < 0 || nx < 0 || ny >= N || nx >= M) continue;
+                            if (external[ny][nx] && map[ny][nx] == 0) {
+                                contact++;
+                            }
+                        }
+                        if (contact >= 2) {
+                            meltList.add(new int[]{i, j});
+                        }
+                    }
+                }
+            }
+            for (int[] pos : meltList) {
+                int y = pos[0], x = pos[1];
+                map[y][x] = 0;
+                cheeseCount--;
+            }
+
+            time++;
+        }
+
+        System.out.println(time);
+    }
+
+    static void markExternalAir() {
+        Queue<int[]> q = new LinkedList<>();
+        boolean[][] visited = new boolean[N][M];
+        q.offer(new int[]{0, 0});
+        visited[0][0] = true;
+        external[0][0] = true;
+
+        while (!q.isEmpty()) {
+            int[] cur = q.poll();
+            int y = cur[0], x = cur[1];
+            for (int d = 0; d < 4; d++) {
+                int ny = y + dy[d];
+                int nx = x + dx[d];
+                if (ny < 0 || nx < 0 || ny >= N || nx >= M) continue;
+                if (visited[ny][nx]) continue;
+                if (map[ny][nx] == 1) {
+                    continue;
+                }
+                visited[ny][nx] = true;
+                external[ny][nx] = true;
+                q.offer(new int[]{ny, nx});
+            }
+        }
+    }
+}
+```