BFS level-order traversal
Return the level-order traversal of a binary tree as a list of lists.
Employee Hierarchy
Build an employee hierarchy tree and compute the total number of direct and indirect reports for each employee.
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.
Tree inorder generator
Write a generator function that yields a binary tree's node values in inorder traversal.
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.
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.
Binary tree left side view
Given a binary tree, return the leftmost node's value at each depth, from top to bottom.
Vertical Order Traversal
Compute the vertical order traversal of a binary tree, grouping nodes by column and row.
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.
Graph Valid Tree
Determine if n nodes and an edge list form a valid tree (connected and acyclic).
Showing 21 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.