[20250718] BOJ / G3 / 다리 만들기 / 이종환

Author: 0224LJH

0224LJH/202507/18 BOJ 다리 만들기 .md

@@ -0,0 +1,130 @@
+```java
+import java.awt.*;
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.*;
+
+public class Main {
+    static int[][] arr;
+    static boolean[][] visited;
+    static int[] dy = {-1,0,1,0};
+    static int[] dx = {0,1,0,-1};
+    static int size;
+    static final int LAND = 1;
+    static final int WATER = 0;
+
+    public static void main(String[] args) throws IOException {
+        init();
+        int result = process();
+        System.out.println(result);
+    }
+
+    private static void init() throws IOException {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        size = Integer.parseInt(br.readLine());
+        arr = new int[size][size];
+
+        for (int i = 0; i < size; i++){
+            StringTokenizer st = new StringTokenizer(br.readLine());
+            for (int j = 0; j < size; j++){
+                arr[i][j] = Integer.parseInt(st.nextToken());
+            }
+        }
+    }
+
+    private static int process() {
+        // 모든 섬들을 서로 다른 번호로 표시
+        visited = new boolean[size][size];
+        int islandNum = 2;
+
+        for (int i = 0; i < size; i++){
+            for (int j = 0; j < size; j++){
+                if (arr[i][j] == LAND && !visited[i][j]){
+                    markIsland(i, j, islandNum);
+                    islandNum++;
+                }
+            }
+        }
+
+        // 각 섬에서 다른 섬으로 가는 최단 거리 찾기
+        int minDistance = Integer.MAX_VALUE;
+
+        for (int currentIsland = 2; currentIsland < islandNum; currentIsland++) {
+            int distance = bfsFromIsland(currentIsland);
+            minDistance = Math.min(minDistance, distance);
+        }
+
+        return minDistance;
+    }
+
+    private static void markIsland(int y, int x, int islandNum) {
+        Queue<Point> q = new LinkedList<>();
+        arr[y][x] = islandNum;
+        q.add(new Point(x, y));
+        visited[y][x] = true;
+
+        while (!q.isEmpty()){
+            Point p = q.poll();
+            for (int i = 0; i < 4; i++) {
+                int nx = p.x + dx[i];
+                int ny = p.y + dy[i];
+                if (ny < 0 || ny >= size || nx < 0 || nx >= size) continue;
+                if (visited[ny][nx] || arr[ny][nx] != LAND) continue;
+
+                visited[ny][nx] = true;
+                arr[ny][nx] = islandNum;
+                q.add(new Point(nx, ny));
+            }
+        }
+    }
+
+    private static int bfsFromIsland(int startIsland) {
+        Queue<Point> queue = new LinkedList<>();
+        boolean[][] bfsVisited = new boolean[size][size];
+
+        // 시작 섬의 모든 셀을 큐에 추가
+        for (int i = 0; i < size; i++){
+            for (int j = 0; j < size; j++){
+                if (arr[i][j] == startIsland){
+                    queue.add(new Point(j, i));
+                    bfsVisited[i][j] = true;
+                }
+            }
+        }
+
+        int distance = 0;
+
+        while (!queue.isEmpty()) {
+            int qSize = queue.size();
+
+            for (int i = 0; i < qSize; i++) {
+                Point p = queue.poll();
+
+                for (int k = 0; k < 4; k++) {
+                    int nx = p.x + dx[k];
+                    int ny = p.y + dy[k];
+
+                    if (nx < 0 || ny < 0 || nx >= size || ny >= size) continue;
+                    if (bfsVisited[ny][nx]) continue;
+
+                    // 다른 섬을 찾았다면 거리 반환
+                    if (arr[ny][nx] >= 2 && arr[ny][nx] != startIsland) {
+                        return distance;
+                    }
+
+                    // 물이면 다음 레벨로 확장
+                    if (arr[ny][nx] == WATER) {
+                        bfsVisited[ny][nx] = true;
+                        queue.add(new Point(nx, ny));
+                    }
+                }
+            }
+            distance++;
+        }
+
+        return Integer.MAX_VALUE;
+    }
+}
+
+```