Reverse Each Alphanumeric Run
Reverse every maximal run of alphanumeric characters (A–Z, a–z, 0–9) in a string, keeping every other character where it is.
reverseRuns("ab-cd ef") -> "ba-dc fe"
reverseRuns("hello, world!") -> "olleh, dlrow!"
reverseRuns("a1b2 c3") -> "2b1a 3c"Hints
Hint 1
Walk the string; when you hit an alphanumeric character, scan forward to the end of the run, reverse that slice, and continue after it.
Hint 2
In a language with mutable arrays, reverse in place with two pointers; otherwise collect pieces and join.