[20260320] BOJ / G3 / 다리 만들기 / 이준희

JHLEE325/202603/20 BOJ G3 다리 만들기.md

@@ -0,0 +1,101 @@
+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+
+    static int N;
+    static int[][] map;
+    static boolean[][] visited;
+    static int[] dx = {-1, 1, 0, 0};
+    static int[] dy = {0, 0, -1, 1};
+    static int minDist = Integer.MAX_VALUE;
+
+    public static void main(String[] args) throws Exception {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        N = Integer.parseInt(br.readLine());
+        map = new int[N][N];
+        visited = new boolean[N][N];
+
+        for (int i = 0; i < N; i++) {
+            StringTokenizer st = new StringTokenizer(br.readLine());
+            for (int j = 0; j < N; j++) {
+                map[i][j] = Integer.parseInt(st.nextToken());
+            }
+        }
+
+        int islandIdx = 2;
+        for (int i = 0; i < N; i++) {
+            for (int j = 0; j < N; j++) {
+                if (map[i][j] == 1) {
+                    numbering(i, j, islandIdx++);
+                }
+            }
+        }
+
+        for (int i = 2; i < islandIdx; i++) {
+            bfs(i);
+        }
+
+        System.out.println(minDist);
+    }
+
+    static void numbering(int r, int c, int idx) {
+        Deque<int[]> q = new ArrayDeque<>();
+        q.add(new int[]{r, c});
+        map[r][c] = idx;
+        visited[r][c] = true;
+
+        while (!q.isEmpty()) {
+            int[] cur = q.poll();
+            for (int i = 0; i < 4; i++) {
+                int nx = cur[0] + dx[i];
+                int ny = cur[1] + dy[i];
+                if (nx >= 0 && nx < N && ny >= 0 && ny < N && !visited[nx][ny] && map[nx][ny] == 1) {
+                    visited[nx][ny] = true;
+                    map[nx][ny] = idx;
+                    q.add(new int[]{nx, ny});
+                }
+            }
+        }
+    }
+
+    static void bfs(int curIdx) {
+        Deque<int[]> q = new ArrayDeque<>();
+        boolean[][] check = new boolean[N][N];
+
+        for (int i = 0; i < N; i++) {
+            for (int j = 0; j < N; j++) {
+                if (map[i][j] == curIdx) {
+                    check[i][j] = true;
+                    q.add(new int[]{i, j, 0});
+                }
+            }
+        }
+
+        while (!q.isEmpty()) {
+            int[] cur = q.poll();
+            int r = cur[0];
+            int c = cur[1];
+            int dist = cur[2];
+
+            if (dist >= minDist) break;
+
+            for (int i = 0; i < 4; i++) {
+                int nx = r + dx[i];
+                int ny = c + dy[i];
+
+                if (nx >= 0 && nx < N && ny >= 0 && ny < N && !check[nx][ny]) {
+                    if (map[nx][ny] == 0) {
+                        check[nx][ny] = true;
+                        q.add(new int[]{nx, ny, dist + 1});
+                    } else if (map[nx][ny] != curIdx) {
+                        minDist = Math.min(minDist, dist);
+                        return;
+                    }
+                }
+            }
+        }
+    }
+}
+```