Longest Substring with K Repeating Characters
Return the length of the longest substring of a given string in which every character appears at least K times.
Run-length encoding
Compress consecutive identical characters, e.g. 'aaabbc' → 'a3b2c1'.
Custom Sort String
Given a string s and an order string, reorder s so that characters that appear in order come first in that order, and all other characters are appended in stable original order.
Parse key-value lines
Parse structured key-value lines into a dictionary with support for quoted values and escaped characters.
Edit Distance (Levenshtein Distance)
Implement the classic edit distance algorithm to find the minimum number of single-character edits required to transform one string into another.
Minimum Genetic Mutation
Implement a function to compute the minimum number of single-character mutations needed to transform one gene string into another, using a given bank of valid mutations.
Partition Labels
Partition a string into maximal parts where each character appears in only one part, returning part lengths.
Character Replacement Window
Given a string and a number k, find the length of the longest substring that can be made uniform by replacing at most k characters.
Longest Substring with At Most K Distinct Characters
Given a string and an integer k, find the length of the longest substring that contains at most k distinct characters.
Longest Repeating Character Replacement
Given a string and an integer k, return the length of the longest substring that can be made of identical characters after at most k replacements.
Base64 Encode Decode
Implement Base64 encoding and decoding functions that handle padding and all standard characters.
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Guide: free Python coding challenges
Practice Python by solving problems
PythonSkillset challenges are hands-on coding exercises from beginner to advanced. Open a challenge, read the problem, write Python in the split-pane editor, and run tests with Pyodide — no install required.
How to use the arena
- Pick a category — basics, algorithms, strings, and more
- Open a challenge, read the statement, and edit the starter code
- Run tests, fix failures, then try a related quiz or tutorial lesson
Challenges vs tutorials and quizzes
Challenges test what you can build under constraints. For guided teaching, use our Python tutorials. For quick checks, try quizzes or copy snippets from code samples.