[백준 2589] 보물섬 - JAVA // le_effort//

일반적인 bfs와 달리 각 정점 ( 위 문제에선 L) 을 기준으로 다 bfs를 진행주면 된다.

 
            import java.io.*;
import java.util.*;
public class Main {
    static int n,m;
    static int max = 0;
    static int dist[][];
    static int dx[] = {0,0,1,-1};
    static int dy[] = {1,-1,0,0};
    static Character map [][];
    static boolean visited[][];
    static ArrayList<Node>list = new ArrayList<>();
    public static void main(String[] args) throws IOException{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        
        String[] t = br.readLine().split(" ");
        n = Integer.parseInt(t[0]);
        m = Integer.parseInt(t[1]);
        
        map = new Character [n][m];
        visited = new boolean[n][m];
        dist = new int[n][m];
        for(int i=0; i<n; i++) {
            String str = br.readLine();
            for(int j=0; j<m; j++) {
                map[i][j]= str.charAt(j);
                if(map[i][j]=='L') {
                    list.add(new Node(i,j));
                }
            }
        }
        for(int i=0; i<list.size(); i++) {
            Node a = list.get(i);
            visited = new boolean[n][m];
            bfs(a);
        }
        System.out.println(max);
        
    }
    public static void bfs(Node o) {
        Queue<Node> q = new LinkedList<>();
        q.add(o);
        visited[o.x][o.y] = true;
        dist = new int[n][m];
        while(!q.isEmpty()) {
            Node a = q.poll();
            for(int i=0; i<4; i++) {
                int nx = a.x+dx[i];
                int ny = a.y+dy[i];
                if(nx>=0 && ny>=0 && nx<n && ny<m) {
                    if(map[nx][ny]=='L' && !visited[nx][ny]) {
                        visited[nx][ny]= true;
                        dist[nx][ny] = dist[a.x][a.y]+1;
                        q.add(new Node(nx,ny));
                    }
                }
            }
        }
        for(int i=0; i<n; i++) {
            for(int j=0; j<m; j++) {
                max = Math.max(max, dist[i][j]);
            }
        }
    }
}
class Node{
    int x,y;
    Node(int x, int y){
        this.x=x;
        this.y=y;
    }
}