Given a string s, reverse the order of its digit characters while leaving every other character where it is. Return the new string.
Examples
Input: s = "a1b2c3"
Output: "a3b2c1"
Input: s = "2024-06-15"
Output: "5160-42-02"
Explanation: the digits 2,0,2,4,0,6,1,5 are written back in reverse into the digit slots.
Constraints
0 <= len(s) <= 10**5- Target: O(n) time; one character buffer of size n is fine.
Goals
- Skip characters that do not satisfy a predicate from both ends
- Swap matching positions in a mutable buffer