L1 · FoundationsNumbers & loops~3 min · 6 tests

Check an Armstrong Number

Check whether a number equals the sum of its digits each raised to the number of digits, like 153 = 1³+5³+3³. Python loop practice with live tests.

The problem

An Armstrong number equals the sum of its digits, each raised to the power of the number of digits: 153 = 1³ + 5³ + 3³.

Return True if n (a non-negative integer) is one.

Examples

Example 1
Input
```
is_armstrong(153)
```
Expected output
```
True
```
Example 2
Input
```
is_armstrong(123)
```
Expected output
```
False
```

+ 4 hidden tests on Submit.

Edge cases to ask about

Single digits are all Armstrong numbers
Zero

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 · is_armstrong

def is_armstrong(n):
    """True if n is an Armstrong number."""
    # 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
Digits list + sum of powers	O(d)	O(d)	d = number of digits.

Walkthrough of the optimal approach (try it yourself first)

Find the number of digits k, raise each digit to k, add them up and compare with n. Here str(n) is the clearest way to get the digits.

Complexity: O(log n) time, O(log n) space. Work and the digit list are proportional to the number of digits.

Reveal the reference solution

def is_armstrong(n):
    digits = [int(d) for d in str(n)]
    power = len(digits)
    return sum(d ** power for d in digits) == n

Follow-ups interviewers ask

List every Armstrong number below 100,000.

Frequently asked interview questions

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

What is the time complexity of Check an Armstrong Number in Python?

The optimal solution runs in O(log n) time and O(log n) auxiliary space. Work and the digit list are proportional to the number of digits.

What follow-up questions do interviewers ask about Check an Armstrong Number?

List every Armstrong number below 100,000.