Reverse the order of the words in a string while trimming and collapsing spaces. Test your code, then compare with the explained solution. Free online practice.

Reverse Words in a String

Two Sum II - Input Array Is Sorted

Find All Duplicates in an Array

Reverse the order of the words in a string while trimming and collapsing spaces.

Given a string `s`, reverse the order of its words. A word is a maximal sequence of non-space characters. When you build the answer, remove any leading or trailing spaces and collapse every run of multiple spaces between words into a single space in the returned string. See the examples and constraints below, then consider the follow-up about solving it in-place.

**Input / output**
- Input: `s: string`
- Output: `string`

## Examples
1. `s = "the sky is blue"` returns `"blue is sky the"`.
2. `s = "  hello world  "` returns `"world hello"`.
3. `s = "a   good    example"` returns `"example good a"`.

## Constraints
- `1 <= s.length <= 10^4`
- `s` contains English letters, digits, punctuation, and spaces.
- A word is any maximal contiguous block of non-space characters.

## Follow-up
Could you solve it in-place with `O(1)` extra space in a language that supports mutable fixed-size character arrays?

A direct approach is to split the string into words, which automatically drops extra spaces, then reverse the word list and join it back together with a single space.

Use whitespace tokenization first

To avoid relying on a built-in split-on-whitespace helper, walk from right to left. Skip trailing spaces, mark the end of the current word, move left until the previous space, append that word, and repeat. Time: O(n). Space: O(n) for the output words/result.