L1 · FoundationsText basics~2 min · 4 tests

Check If a Sentence Is a Pangram

Q: What is the time complexity of Check If a Sentence Is a Pangram in Python?

The optimal solution runs in O(n) time and O(1) auxiliary space. One pass to build the set; the set is bounded by the character set size, not by n.

Q: What is the brute-force approach, and how do you optimise it?

Check each letter with `in`: O(26 · n) time, O(1) space. Set subset test: O(n) time, O(1) space. At most 26 + charset entries.

Check whether a sentence uses every letter of the alphabet at least once with a set in O(n). Includes early exit and case handling. Python practice.

The problem

Return True if sentence contains every letter a–z at least once (ignoring case).

Examples

Example 1

Input

is_pangram('The quick brown fox jumps over the lazy dog')

Expected output

True

Example 2
Input
```
is_pangram('Hello world')
```
Expected output
```
False
```

+ 2 hidden tests on Submit.

Edge cases to ask about

Upper case
Punctuation
Empty

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_pangram

def is_pangram(sentence):
    """True if every letter a-z appears."""
    # Write your solution here
    pass

⌘/Ctrl + Enter runs the examples

Your code runs in real CPython inside your browser — nothing is sent anywhere. The first run downloads the interpreter (about 6 MB, once). Your code is saved on this device as you type.

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
Check each letter with `in`	O(26 · n)	O(1)
bestSet subset test	O(n)	O(1)	At most 26 + charset entries.

Walkthrough of the optimal approach (try it yourself first)

Lower-case the sentence, make a set of its characters, and check the alphabet is a subset (<=). The set can hold at most a few dozen distinct characters, so its space is O(1) even for a huge sentence.

Complexity: O(n) time, O(1) space. One pass to build the set; the set is bounded by the character set size, not by n.

Reveal the reference solution

import string

def is_pangram(sentence):
    return set(string.ascii_lowercase) <= set(sentence.lower())

Follow-ups interviewers ask

Return the missing letters.

Frequently asked interview questions

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

What is the time complexity of Check If a Sentence Is a Pangram in Python?