Reverse Words in a String (Preserve Spaces, In-Place)

Reverse the word order in a string. Follow-ups: rewrite to preserve the original number of spaces between every position, and reduce extra space below `O(n)`. Requirements Given a string s, reverse the order of words. A word is a maximal substring of non-space characters. def reverseWords(s: str) -> str: ... Follow-ups asked: Write multiple test cases for your first solution and run them. Modify the first version to preserve the exact original spacing (the number of spaces between word positions must match the input). Optimize complexity — first your solution's, then ask whether you can do it in-place (O(1) extra space). The reported round was C++-specific; the candidate's reverse(begin, end) twice approach was accepted as a passable in-place solution but the interviewer probed for whether that matched their intent. Notes The classic O(1) extra-space pattern is: (1) reverse the entire string in place, (2) reverse each word in place. Works on a mutable character array. For the "preserve spacing" variant: collect the words and the run-lengths of spaces separately, then interleave reversed-word-list with the original space-run sequence. For the C++ in-place version, std::reverse(first, last) plus a two-pointer scan to find word boundaries is the standard answer. Time O(n); space O(1) for in-place, O(n) for the split-and-join approach. Common bug: handling consecutive spaces, leading spaces, or trailing spaces — clarify the trim-or-preserve policy with the interviewer up front. The canonical formulation trims whitespace; the reported variant explicitly preserves the original space layout, which is the harder follow-up. Preparation Code the in-place reverse-then-reverse-words version in C++ (or your interview language) until it is second nature. Drill the "preserve spaces" variant separately — most candidates have not seen it. Practice on inputs with multiple spaces between words, leading/trailing spaces, and a single word. Be ready to argue the complexity of each variant and why the two-reverse trick works.