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

public int[][] updateMatrix(int[][] mat) {

int numRows = mat.length;

int numCols = mat[0].length;

int[][] distances = new int[numRows][numCols];

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

for (int i = 0; i < numRows; i++) {

for (int j = 0; j < numCols; j++) {

if (mat[i][j] == 0) {

queue.add(new int[]{i, j});

} else {

distances[i][j] = Integer.MAX_VALUE;

}

}

}

while (!queue.isEmpty()) {

int[] removed = queue.remove();

int currX = removed[0];

int currY = removed[1];

for (int[] dir : DIRS) {

int newX = currX + dir[0];

int newY = currY + dir[1];

if (newX >= 0 && newY >= 0 && newX < numRows && newY < numCols && distances[newX][newY] > distances[currX][currY] + 1) {

queue.add(new int[]{newX, newY});

distances[newX][newY] = distances[currX][currY] + 1;

}

}

}

return distances;

}