[20250719] BOJ / G4 / 빙산 / 이준희

JHLEE325/202507/19 BOJ G4 빙산.md

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+```java
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.util.*;
+
+public class Main {
+
+    static int n, m;
+    static int[][] map, meltcount;
+    static boolean[][] visited;
+    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 = new StringTokenizer(br.readLine());
+
+        n = Integer.parseInt(st.nextToken());
+        m = Integer.parseInt(st.nextToken());
+
+        map = new int[n][m];
+        visited = new boolean[n][m];
+
+        for (int i = 0; i < n; i++) {
+            st = new StringTokenizer(br.readLine());
+            for (int j = 0; j < m; j++) {
+                int num = Integer.parseInt(st.nextToken());
+                map[i][j] = num;
+            }
+        }
+
+        int year = 0;
+        while (true) {
+            int count = countice();
+
+            if (count >= 2) {
+                System.out.println(year);
+                return;
+            }
+
+            if (count == 0) {
+                System.out.println(0);
+                return;
+            }
+
+            melt();
+            year++;
+        }
+    }
+
+    static void bfs(int x, int y) {
+        Queue<int[]> q = new LinkedList<>();
+        q.offer(new int[]{x, y});
+        visited[x][y] = true;
+
+        while (!q.isEmpty()) {
+            int[] now = q.poll();
+            for (int d = 0; d < 4; d++) {
+                int dy = now[0] + dir[d][0];
+                int dx = now[1] + dir[d][1];
+
+                if (dy >= 0 && dx >= 0 && dy < n && dx < m) {
+                    if (map[dy][dx] > 0 && !visited[dy][dx]) {
+                        visited[dy][dx] = true;
+                        q.offer(new int[]{dy, dx});
+                    }
+                }
+            }
+        }
+    }
+
+    static int countice() {
+        visited = new boolean[n][m];
+        int count = 0;
+
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                if (map[i][j] > 0 && !visited[i][j]) {
+                    bfs(i, j);
+                    count++;
+                }
+            }
+        }
+        return count;
+    }
+
+    static void melt() {
+        meltcount = new int[n][m];
+
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                if (map[i][j] > 0) {
+                    int sea = 0;
+                    for (int d = 0; d < 4; d++) {
+                        int dy = i + dir[d][0];
+                        int dx = j + dir[d][1];
+                        if (dy >= 0 && dx >= 0 && dy < n && dx < m) {
+                            if (map[dy][dx] == 0)
+                                sea++;
+                        }
+                    }
+                    meltcount[i][j] = sea;
+                }
+            }
+        }
+
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                map[i][j] -= meltcount[i][j];
+                if (map[i][j] < 0)
+                    map[i][j] = 0;
+            }
+        }
+    }
+}
+```