ZeroOneMatrix.java

class Solution {

    private static final int[][] DIRS = new int[][] {
        new int[] {-1,0},
        new int[] {1,0},
        new int[] {0,-1},
        new int[] {0,1}
    };

    public int[][] updateMatrix(int[][] mat) {
        int m = mat.length;
        int n = mat[0].length;
        int[][] result = new int[m][n];
        Queue<Cell> queue = new LinkedList<>();
        for (int r = 0; r < m; r++) {
            for (int c = 0; c < n; c++) {
                if (mat[r][c] == 0) {
                    var cell = new Cell(r, c, 0);
                    queue.offer(cell);
                }
            }
        }
        while (!queue.isEmpty()) {
            var curr = queue.poll();
            for (var dir : DIRS) {
                int nr = curr.r + dir[0];
                int nc = curr.c + dir[1];
                if (isInbound(mat, nr, nc) && mat[nr][nc] == 1) {
                    mat[nr][nc] = 0;
                    int distance = curr.distance + 1;
                    result[nr][nc] = distance;
                    var cell = new Cell(nr, nc, distance);
                    queue.offer(cell);
                }
            }
        }
        return result;
    }

    private boolean isInbound(int[][] grid, int r, int c) {
        return r >= 0 && r < grid.length && c >= 0 && c < grid[r].length;
    }

    private record Cell(int r, int c, int distance) {

    }
}