House Robber
Given a list of house values, return the maximum sum you can rob without robbing two adjacent houses.
Unique Paths in a Grid
Count the number of unique paths from the top-left corner to the bottom-right corner of a grid, moving only right and down.
Triangle Minimum Path
Compute the minimum path sum from top to bottom of a triangle given as a list of lists.
Shortest Unsorted Continuous Subarray
Given an array of integers, return the length of the shortest contiguous subarray whose sorting makes the whole array sorted.
Derangement count
Implement a function to count derangements of n items using the classic recurrence.
Tiling dominoes count
Given a 2 x n board, count the distinct tilings using 2 x 1 dominoes.
Binary Search Tree Class
Build a BinarySearchTree class and a sequence runner that executes a list of operations.
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.
Cycle Detection in Undirected Graph
Write a function that detects if an undirected graph contains a cycle.
Find the Town Judge
Given n people and a trust array, return the town judge or -1.
Find center of star graph
Write a function that finds the center node of a star graph from its list of edges in O(1) time.
Keys and Rooms
A classic graph traversal challenge: check if all rooms are reachable from room 0 using keys found in visited rooms.
Clique Detection
Given an undirected graph and a list of vertices, check if every pair of distinct vertices in the list is connected by an edge.
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.
Showing 433–456 of 556 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.