Reverse Words in a String

Intuition

The messy part of this problem is the irregular spacing, so the cleanest mental model is to first recover the pure list of words and forget about the original whitespace entirely. Once we hold the words as separate items, reversing their order and rejoining with one space each guarantees the required formatting. Languages with rich string libraries can do this in a couple of lines, but the same idea works with a manual scan.

Algorithm walkthrough

1. 1Scan the string and collect each maximal block of non-space characters as one word, ignoring the gaps between them.
2. 2Discard any empty pieces so leading, trailing, or doubled spaces do not create blank words.
3. 3Reverse the collected list of words.
4. 4Concatenate the words together, inserting a single space between consecutive words.
5. 5Return the resulting string.

Implementation

class Solution:
    def reverseWords(self, s: str) -> str:
        words = s.split()
        words.reverse()
        return ' '.join(words)