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| 1 | +package BFS.P7576; |
| 2 | + |
| 3 | +import java.io.*; |
| 4 | +import java.util.*; |
| 5 | + |
| 6 | +public class Main2 { |
| 7 | + |
| 8 | + static int M, N, zero, cnt; |
| 9 | + static int[][] map; |
| 10 | + static int[] di = {-1, 0, 1, 0}, dj = {0, 1, 0, -1}; |
| 11 | + static Queue<Pos> q = new LinkedList<>(); |
| 12 | + |
| 13 | + public static void main(String[] args) throws Exception { |
| 14 | + System.setIn(new FileInputStream("src/BFS/P7576/input.txt")); |
| 15 | + BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); |
| 16 | + StringTokenizer st = new StringTokenizer(br.readLine()); |
| 17 | + |
| 18 | + M = Integer.parseInt(st.nextToken()); |
| 19 | + N = Integer.parseInt(st.nextToken()); |
| 20 | + map = new int[N][M]; |
| 21 | + for (int i = 0; i < N; i++) { |
| 22 | + st = new StringTokenizer(br.readLine()); |
| 23 | + for (int j = 0; j < M; j++) { |
| 24 | + map[i][j] = Integer.parseInt(st.nextToken()); |
| 25 | + if (map[i][j] == 1) q.offer(new Pos(i, j, 0)); |
| 26 | + else if (map[i][j] == 0) zero ++; |
| 27 | + } |
| 28 | + } |
| 29 | + |
| 30 | + while (!q.isEmpty()) { |
| 31 | + Pos p = q.poll(); |
| 32 | + for (int k = 0; k < 4; k++) { |
| 33 | + int to_i = p.i + di[k]; |
| 34 | + int to_j = p.j + dj[k]; |
| 35 | + if (isValidPath(to_i, to_j) && map[to_i][to_j] == 0) { |
| 36 | + map[to_i][to_j] = 1; |
| 37 | + q.offer(new Pos(to_i, to_j, p.d+1)); |
| 38 | + zero --; |
| 39 | + } |
| 40 | + } |
| 41 | + cnt = p.d; |
| 42 | + } |
| 43 | + |
| 44 | + if (zero > 0) System.out.println(-1); |
| 45 | + else System.out.println(cnt); |
| 46 | + } |
| 47 | + |
| 48 | + static boolean isValidPath(int i, int j) { |
| 49 | + return 0 <= i && i < N && 0 <= j && j < M; |
| 50 | + } |
| 51 | + |
| 52 | + static class Pos { |
| 53 | + int i, j, d; |
| 54 | + |
| 55 | + public Pos(int i, int j, int d) { |
| 56 | + this.i = i; |
| 57 | + this.j = j; |
| 58 | + this.d = d; |
| 59 | + } |
| 60 | + } |
| 61 | +} |
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