# Upside Down Numbers

An upside down number is one that appears the same when flipped `180`

degrees. Given `n`

, return all upside down numbers as strings whose length is `n`

, sorted in lexicographic order.

**Constraints**

`n ≤ 15`

https://binarysearch.com/problems/Upside-Down-Numbers

## Examples

### Example 1

**Input**

- n =
`1`

**Output**

- answer =
`['0', '1', '8']`

### Example 2

**Input**

- n =
`2`

**Output**

- answer =
`['11', '69', '88', '96']`

### Example 3

**Input**

- n =
`3`

**Output**

- answer =
`['101', '111', '181', '609', '619', '689', '808', '818', '888', '906', '916', '986']`

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