Count inversions lite
Implement a function that counts inversions in a list of numbers efficiently.
Radix Sort
Implement LSD radix sort to sort a list of non-negative integers in ascending order.
Decode Ways
Count the number of ways to decode a numeric string into letters using the mapping A=1 to Z=26.
Target Sum Subsets
Write a function that counts the number of subsets of a list of positive integers that sum exactly to a target.
Coin Change Ways
Count the number of distinct combinations of coins that sum to a target amount.
Count Nice Subarrays
Given an array of integers, count the number of contiguous subarrays that contain exactly k odd numbers.
Top K Frequent Elements
Given an integer array and a number k, return the k most frequent elements using a heap-based approach.
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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.