[20250806] BOJ / G4 / 연구소 / 이준희

Author: JHLEE325

JHLEE325/202508/06 BOJ G4 연구소.md

@@ -0,0 +1,99 @@
+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+
+    static int n, m;
+    static int[][] board;
+    static int maxSafe = 0;
+    static int[][] dir = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
+
+    public static void main(String[] args) throws Exception {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        StringTokenizer st;
+
+        st = new StringTokenizer(br.readLine());
+        n = Integer.parseInt(st.nextToken());
+        m = Integer.parseInt(st.nextToken());
+
+        board = new int[n][m];
+        List<Integer> empties = new ArrayList<>();
+        List<Integer> viruses = new ArrayList<>();
+
+        for (int r = 0; r < n; r++) {
+            st = new StringTokenizer(br.readLine());
+            for (int c = 0; c < m; c++) {
+                board[r][c] = Integer.parseInt(st.nextToken());
+                if (board[r][c] == 0) empties.add(r * m + c);
+                else if (board[r][c] == 2) viruses.add(r * m + c);
+            }
+        }
+
+        int E = empties.size();
+
+        for (int i = 0; i < E; i++) {
+            for (int j = i + 1; j < E; j++) {
+                for (int k = j + 1; k < E; k++) {
+                    int[][] tmp = copyBoard(board);
+
+                    placeWall(tmp, empties.get(i));
+                    placeWall(tmp, empties.get(j));
+                    placeWall(tmp, empties.get(k));
+
+                    spreadVirus(tmp, viruses);
+
+                    int safe = countSafe(tmp);
+                    if (safe > maxSafe) maxSafe = safe;
+                }
+            }
+        }
+
+        System.out.println(maxSafe);
+    }
+
+    static int[][] copyBoard(int[][] src) {
+        int[][] dst = new int[n][m];
+        for (int r = 0; r < n; r++) {
+            System.arraycopy(src[r], 0, dst[r], 0, m);
+        }
+        return dst;
+    }
+
+    static void placeWall(int[][] g, int pos) {
+        int r = pos / m, c = pos % m;
+        g[r][c] = 1;
+    }
+
+    static void spreadVirus(int[][] g, List<Integer> viruses) {
+        ArrayDeque<int[]> q = new ArrayDeque<>();
+        for (int v : viruses) {
+            int vr = v / m, vc = v % m;
+            q.add(new int[]{vr, vc});
+        }
+        while (!q.isEmpty()) {
+            int[] cur = q.poll();
+            int y = cur[0], x = cur[1];
+            for (int d = 0; d < 4; d++) {
+                int dy = y + dir[d][0], dx = x + dir[d][1];
+                if (dy < 0 || dy >= n || dx < 0 || dx >= m) continue;
+                if (g[dy][dx] == 0) {
+                    g[dy][dx] = 2;
+                    q.add(new int[]{dy, dx});
+                }
+            }
+        }
+    }
+
+    static int countSafe(int[][] g) {
+        int cnt = 0;
+        for (int r = 0; r < n; r++) {
+            for (int c = 0; c < m; c++) {
+                if (g[r][c] == 0) cnt++;
+            }
+        }
+        return cnt;
+    }
+}
+
+```