A strobogrammatic number is a number that looks the same when rotated 180 degrees (viewed upside down). The valid digits and their rotations are:
0 -> 0
1 -> 1
6 -> 9
8 -> 8
9 -> 6
Write a function `find_strobogrammatic(n)` that takes a positive integer `n` and returns a list of strobogrammatic numbers of exactly length `n`, sorted in ascending order. For `n = 0`, the function should return `['']` (the empty string is considered a strobogrammatic number of length 0). For `n >= 1`, numbers must not have leading zeros (e.g., for n=2, '00' is not allowed). The returned numbers should be represented as strings, not integers.
Examples:
- `find_strobogrammatic(1)` returns `['0', '1', '8']`
- `find_strobogrammatic(2)` returns `['11', '69', '88', '96']`
- `find_strobogrammatic(3)` returns `['101', '111', '181', '609', '619', '689', '808', '818', '888', '906', '916', '986']`
Constraints
1 <= n <= 14 (the number of strobogrammatic numbers is manageable, but do not generate all numbers and filter; construct them directly).
Output list must be sorted in ascending numeric order (as strings). Complexity should be about O(5^(n/2)) time and space.