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.
Symmetric Difference
Write a function that computes the symmetric difference of two lists, returning a sorted list of unique elements.
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.
Function composition
Return a function that applies f after g: compose(f, g)(x) == f(g(x)).
Curry a function
Auto-curry any multi-argument function so it returns partial applications until fully saturated.
Singleton Factory
Implement a factory class that returns a singleton instance per key.
Valid parentheses
Return True if brackets in the string close in the correct order.
Binary search
Return the index of target in a sorted list, or -1 if not present.
Quicksort
Implement quicksort and return a sorted list.
BFS level-order traversal
Return the level-order traversal of a binary tree as a list of lists.
Graph DFS
Return all nodes reachable from a start node via DFS.
Longest increasing subsequence
Return the length of the longest strictly increasing subsequence.
Topological sort (Kahn)
Return a valid topological ordering of tasks, or [] if a cycle exists.
Word ladder length
Return the length of the shortest transformation from beginWord to endWord changing one letter at a time.
Index of peak element
Implement a function that returns the index of any peak element in a given integer array.
Find Peak Element
Implement a function that returns the index of any peak element in an integer array.
Median of Two Sorted Arrays
Given two sorted arrays, return the median of the combined sorted array in O(log(min(n,m))) time.
Pascal Triangle Row
Given a non-negative integer n, return the nth row of Pascal's triangle as a list of integers.
Merge Sort
Implement merge_sort(numbers) that returns a sorted copy of the input list using the merge sort algorithm.
Path Sum II All Paths
Return all root-to-leaf paths where the sum of node values equals a target.
Redundant Connection
Given a list of edges forming a tree plus one extra edge, return the edge that appears last in the input and creates a cycle.
Find Peak Index
Given a list of integers, return the index of any peak element where the value is not smaller than its neighbors.
Showing 145–168 of 371 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.