Extract Hashtags
Extract unique hashtags from a given text string in the order they appear.
Extract mentions
Extract unique @mentions from a string, respecting email-like patterns and punctuation.
Find repeated words
Return a lowercase list of unique words that appear more than once across a given text, ignoring case.
Second Largest Unique Value
Return the second largest distinct integer from a list, or None if it doesn't exist.
All Unique Values Keep Order
Remove duplicates from a list, keeping only the first occurrence of each value while preserving relative order.
Find Second Largest
Find the second largest unique number in a list, or None if it doesn't exist.
Intersection of Two Lists
Given two lists, return a sorted list of unique elements that appear in both lists.
Union of Two Lists
Implement a function that combines two lists and returns only unique elements.
Two Missing Numbers
Given a list of n-2 unique integers from 1 to n, find the two missing numbers efficiently.
One Hot Encode Labels
Given a list of categorical labels, return a list of one-hot encoded vectors based on the sort order of unique labels.
Word to Index Map
Create a function that returns a dictionary mapping each unique word to the index of its first occurrence.
Symmetric Difference
Write a function that computes the symmetric difference of two lists, returning a sorted list of unique elements.
Unique Paths in a Grid
Count the number of unique paths from the top-left corner to the bottom-right corner of a grid, moving only right and down.
Unique Paths with Obstacles
Given a 2D grid with obstacles, count the unique paths from top-left to bottom-right moving only down or right.
Unique Paths in a Grid
Count distinct paths in an m x n grid moving only down or right.
Alien Dictionary Order
Given a sorted list of words in an alien language, derive the order of its unique letters.
Subsets II
Given a collection of integers that might contain duplicates, return all possible unique subsets.
Combination Sum
Given a list of distinct positive integers and a target, return all unique combinations that sum to the target.
Three Sum
Given an array of integers, return all unique triplets that sum to zero.
Four Sum
Find all unique quadruplets in an array that sum to a given target.
Showing 1–20 of 20 challenges
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.