Anagram Dictionary Groups Lite
Group a list of words into anagrams using a dictionary keyed by sorted characters.
Common Keys of Two Dictionaries
Implement a function that finds keys shared by two dictionaries and returns them sorted.
Union of Many Sets
Implement a function that takes any number of sets and returns a sorted list of their union.
Mode of a list via counting
Implement a function that returns the mode of a list, resolving ties by the element that appears first.
Top k keys by count
Given a dictionary mapping keys to counts, return the top k keys with the highest counts, breaking ties alphabetically.
Values that appear once
Return a list of numbers that appear exactly once in the input list, in original order.
Replace keys with a mapping
Write a function that renames keys in a dictionary according to a mapping, with duplicate handling.
Two Sum with Dict
Implement the classic Two Sum problem: return indices of two numbers that add up to a target using a dict.
Anagram Groups by Size
Group a list of words into anagram groups and return them sorted by group size and lexicographically.
Top K Frequent Words
Given a list of words, return the k most frequent words sorted by frequency (descending) and then alphabetically.
Sort by frequency
Sort a list by element frequency descending, with ties broken by order of first occurrence.
Pair with difference K
Count unordered index pairs with absolute difference exactly K, handling duplicates correctly.
Set intersection size
Count how many distinct values appear in both of two given lists.
Symmetric Difference
Write a function that computes the symmetric difference of two lists, returning a sorted list of unique elements.
Disjoint Set Check
Check if two lists are disjoint by verifying they have no common elements.
Subset of another set
Write a function that checks if every element of one set is contained in another.
Frequency sort descending
Write a function that sorts a list by frequency descending while preserving original order for ties.
Count Pairs with Sum
Implement a function that counts the number of distinct pairs in a list summing to a target.
Ransom Note Builder
Given two strings, determine if the ransom note can be formed from the words in the magazine.
Longest Harmonious Subsequence
Given a list of integers, find the length of the longest harmonious subsequence where the difference between maximum and minimum values is exactly 1.
Group by Department
Implement a function that groups a list of employee dictionaries by department, returning a dictionary keyed by department with lists of employee dictionaries.
Revenue by Month
Write a function that groups a list of (date, amount) pairs by year-month and returns total revenue per month as a sorted dictionary.
Pivot sales by product
Write a function that pivots sales records into a dictionary keyed by product with monthly totals.
Bind First Argument
Implement bind_first_arg, a decorator that fixes the first argument of any function.
Showing 265–288 of 556 challenges · easy
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.