Solution.java

import java.util.LinkedList;
import java.util.Queue;

class Solution {
    private static final int[][] DIRECTIONS = new int[][]{{1, 0}, {-1, 0}, {0, 1}, {0, -1}};

    public int[][] updateMatrix(int[][] mat) {
        int n = mat.length, m = mat[0].length;
        int[][] result = new int[n][m];

        Queue<int[]> queue = new LinkedList<>();

        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (mat[i][j] == 0) {
                    queue.add(new int[]{i, j});
                } else {
                    result[i][j] = Integer.MAX_VALUE;
                }
            }
        }


        int steps = 0;
        while (!queue.isEmpty()) {
            int size = queue.size();

            for (int i = 0; i < size; i++) {
                int[] curr = queue.poll();
                int x = curr[0], y = curr[1];

                for (int[] dir : DIRECTIONS) {
                    int a = x + dir[0], b = y + dir[1];

                    if (a >= 0 && a < n && b >= 0 && b < m && result[a][b] == Integer.MAX_VALUE) {
                        result[a][b] = 1 + steps;
                        queue.add(new int[]{a, b});
                    }
                }
            }

            steps++;
        }


        return result;
    }
}