Factorial (iterative)
Compute n! iteratively without recursion.
GCD via Euclid
Compute the greatest common divisor of two positive integers.
Sort List Merge Sort
Write a function that sorts a list of integers using the merge sort algorithm.
Flatten Multidimensional Lists
Write a function that flattens arbitrarily nested lists of integers into a single list.
Employee Hierarchy
Build an employee hierarchy tree and compute the total number of direct and indirect reports for each employee.
Lowest Common Ancestor in a Binary Search Tree
Implement a function to find the lowest common ancestor of two node values in a binary search tree.
Graph DFS Generator
Implement a generator function that performs a depth-first traversal of a graph without recursion.
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).
Derangement count
Implement a function to count derangements of n items using the classic recurrence.
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.
Insert into BST
Implement insertion into a Binary Search Tree while maintaining BST properties.
Range Sum BST
Return the sum of all node values in a BST that lie within a given inclusive range [low, high].
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.
Permutations
Write a function that returns every permutation of the elements in the input list.
Power set from set
Write a function to return the power set of a given list of distinct elements.
Showing 1–24 of 24 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.