Return all non-negative integers of length `n` such that the absolute difference between every two consecutive digits is `k`.

Note that every number in the answer must not have leading zeros. For example, `01` has one leading zero and is invalid.

You may return the answer in any order.

Example 1:

    Input: n = 3, k = 7
    Output: [181,292,707,818,929]
    Explanation: Note that 070 is not a valid number, because it has leading zeroes.

Example 2:

    Input: n = 2, k = 1
    Output: [10,12,21,23,32,34,43,45,54,56,65,67,76,78,87,89,98]

Constraints:

- `2 <= n <= 9`
- `0 <= k <= 9`