Factorial (iterative)
Compute n! iteratively without recursion.
GCD via Euclid
Compute the greatest common divisor of two positive integers.
Fibonacci(n)
Return the nth Fibonacci number efficiently.
Flatten nested list
Yield every integer from an arbitrarily nested list, depth-first.
Hash map merge
Write a function that merges two dictionaries recursively, combining values and preserving structure.
Quicksort
Implement quicksort and return a sorted list.
Graph DFS
Return all nodes reachable from a start node via DFS.
Employee Hierarchy
Build an employee hierarchy tree and compute the total number of direct and indirect reports for each employee.
Merge Sort
Implement merge_sort(numbers) that returns a sorted copy of the input list using the merge sort algorithm.
Lucas Sequence
Implement a function to compute the n-th Lucas number using iteration or recursion with memoization.
Partition function
Write a function that returns the number of ways to write a positive integer as a sum of positive integers (order irrelevant).
Binary Tree Inorder Traversal
Implement an inorder traversal function that returns node values in left-root-right order.
Preorder Traversal
Implement a function that returns the preorder traversal values of a binary tree.
Postorder Traversal
Implement a function that returns the postorder traversal of a binary tree as a list of node values.
Maximum depth of tree
Implement max_depth(root) to return the maximum depth of a binary tree.
Minimum Depth of Tree
Given a binary tree, compute the minimum depth from the root to the nearest leaf node.
Symmetric Tree Check
Write a function that checks whether a binary tree is symmetric (a mirror of itself).
Same Tree Check
Write a function that checks whether two binary trees are identical in structure and node values.
Lowest Common Ancestor in a Binary Tree
Implement a function to find the lowest common ancestor (LCA) of two nodes in a binary tree.
Sum Root to Leaf Numbers
Given the root of a binary tree, compute the total sum of all root-to-leaf numbers.
Delete Node in BST
Implement a function that deletes a key from a binary search tree and returns the new root.
Insert into BST
Implement insertion into a Binary Search Tree while maintaining BST properties.
Trim BST to range
Implement a function to trim a BST to only retain nodes with values in a given inclusive range.
Cycle Detection in a Directed Graph
Use DFS with a recursion stack to detect cycles in a directed graph.
Wildcard Match (Simple)
Write a function that checks whether a string matches a pattern with '*' and '?' wildcards.
Permutation Generator
Write a function that returns all permutations of a list of distinct integers.
Combination Generator
Write a recursive function that returns all combinations of length k from a list of distinct integers.
Showing 27 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.