L1 · FoundationsText basics~2 min · 4 tests

Reverse the Words in a Sentence

Reverse the order of words in a sentence with split() and join(), collapsing extra spaces. A frequent Python interview question with live tests.

The problem

Return the words of sentence in reverse order, separated by single spaces. Extra spaces anywhere are dropped.

"I love Python" → "Python love I".

Examples

Example 1

Input

reverse_words('I love Python')

Expected output

'Python love I'

Example 2

Input

reverse_words('  hello   world  ')

Expected output

'world hello'

+ 2 hidden tests on Submit.

Edge cases to ask about

Extra spaces
Single word
Empty string

Hints

0/3

How an interviewer scores this

0/9

1. Understand the problemRestate it, ask about edge cases and input size.
2. Write a brute-force solutionCorrect first, clever later.
3. Get the correct outputautoAll visible examples pass.
4. Analyse time complexityautoCommit to a Big-O in the Complexity Lab.
5. Analyse space complexityautoExtra memory, not the input.
6. Identify the bottleneckautoMeasure your code — where does it bend?
7. OptimiseUsually: a set or dict instead of a scan.
8. Explain why it worksSay it out loud to Solvi.
9. Test the edge casesautoSubmit passes every hidden test.

Python 3.13 · reverse_words

def reverse_words(sentence):
    """Words in reverse order, single-spaced."""
    # Write your solution here
    pass

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Complexity Lab

What does this cost as n grows?

Interviewers score the analysis as much as the code. Commit to an answer first — then check it, and read why.

Time complexity of the optimal solution

Space complexity (extra memory)

Pick both to reveal the answer.

From brute force to optimal

The progression an interviewer wants to hear, one step at a time.

Approach	Time	Space	Idea
split → reverse → join	O(n)	O(n)	split() with no argument collapses whitespace.

Walkthrough of the optimal approach (try it yourself first)

sentence.split() (no argument) splits on any run of whitespace and drops leading/trailing spaces. Reverse the list and " ".join it back. split(" ") would keep empty strings for the extra spaces — a common slip.

Complexity: O(n) time, O(n) space. Splitting and joining each touch every character once.

Reveal the reference solution

def reverse_words(sentence):
    return " ".join(reversed(sentence.split()))

Follow-ups interviewers ask

Reverse each word but keep word order.

Frequently asked interview questions

Core interview concepts, complexities, and follow-ups scored by hiring teams.

What is the time complexity of Reverse the Words in a Sentence in Python?

The optimal solution runs in O(n) time and O(n) auxiliary space. Splitting and joining each touch every character once.

What follow-up questions do interviewers ask about Reverse the Words in a Sentence?

Reverse each word but keep word order.