Count word occurrences
Write a function that takes a sentence and returns a dictionary of word counts.
Garbage Collection Hint
Write a function that predicts when an object is garbage collected based on reference counting.
Most Common Character
Return the character that appears most frequently in a string, breaking ties by earliest occurrence.
Parse Log Line
Write a function that parses a log line and returns a dictionary with timestamp, level, and message.
Parse key=value pairs
Implement a parser that converts a space-separated 'key=value' string into a Python dictionary, supporting quoted values.
Replace template variables
Implement a function that replaces {{variable}} placeholders in a string using a dictionary, leaving unknown placeholders intact.
Two Sum
Return indices (i, j) with i < j such that nums[i] + nums[j] == target.
Word frequency
Return a dict mapping each word to its count in the sentence.
Group anagrams
Group words that are anagrams of each other.
First non-repeating character
Find the index of the first character that appears only once.
Most frequent element
Return the element that appears most often in a list.
Subarray sum equals K
Count the number of contiguous subarrays whose sum equals k.
Merge dicts summing values
Write a function that merges two dictionaries by summing values for duplicated keys.
Are two lists the same multiset
Write a function that checks if two lists contain the same elements with the same multiplicities, ignoring order.
Word to Index Map
Create a function that returns a dictionary mapping each unique word to the index of its first occurrence.
Group names by first letter
Given a list of names, return a dictionary mapping each first letter to all names starting with that letter in original order.
Missing keys default zero
Write a function to sum numeric values from dictionaries, treating missing keys as zero.
Keys Sorted by Value Descending
Given a dictionary mapping strings to integers, return a list of keys sorted by value descending, and when values tie, alphabetically ascending.
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.
LRU cache decorator
Implement @lru_cache(maxsize=N) for unary functions using OrderedDict.
Key error handler
Implement a safe dictionary access function that returns a default value on missing keys.
Word Break DP
Implement a function to check if a string can be segmented into space-separated dictionary words.
Vertical Order Traversal
Compute the vertical order traversal of a binary tree, grouping nodes by column and row.
Alien Dictionary Order
Given a sorted list of words in an alien language, derive the order of its unique letters.
Showing 38 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.