Nested get with dotted path
Implement a function that safely retrieves a value from a deeply nested dictionary using a dot-separated path, returning a default if any key is missing.
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.
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.
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.
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.
Hash map merge
Write a function that merges two dictionaries recursively, combining values and preserving structure.
Ransom Note Builder
Given two strings, determine if the ransom note can be formed from the words in the magazine.
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.
Singleton Factory
Implement a factory class that returns a singleton instance per key.
LRU cache decorator
Implement @lru_cache(maxsize=N) for unary functions using OrderedDict.
Top N per group
Implement top_n_per_group that returns the top N scores for each group from a list of (group, score) pairs.
Employees earning more than manager
Given employee records with manager IDs, find those who earn more than their direct manager.
Key error handler
Implement a safe dictionary access function that returns a default value on missing keys.
Parse bit field flags
Write a function that unpacks a bit field integer into a dict of named boolean flags.
Showing 25–48 of 61 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.