BFS level-order traversal
Return the level-order traversal of a binary tree as a list of lists.
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.
AST Visitor Lite
Implement a depth-first traversal of a simplified AST and return identifier names in order.
Level Order Traversal
Implement a function that performs a level order traversal of a binary tree and returns node values as a list of lists.
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.
Trim BST to range
Implement a function to trim a BST to only retain nodes with values in a given inclusive range.
Validate BST
Implement a function to determine if a binary tree is a valid Binary Search Tree.
Kth Smallest in BST
Implement a function that returns the k-th smallest value in a binary search tree.
Count Complete Tree Nodes
Given a complete binary tree, return its node count faster than O(n) time.
Zigzag Level Order Traversal
Implement a function that returns the zigzag level-order traversal of a binary tree.
Maximum Width of a Binary Tree
Given the root of a binary tree, compute its maximum width (the maximum number of nodes in any level, counting null positions).
Graph Valid Tree
Determine if n nodes and an edge list form a valid tree (connected and acyclic).
Prim's Minimum Spanning Tree
Given a connected undirected weighted graph, compute the total weight of its minimum spanning tree using Prim's algorithm.
Kruskal MST
Implement Kruskal's algorithm to compute the total weight of a minimum spanning tree in a connected undirected graph.
Minimum Height Trees
Given an undirected tree, find all root nodes that minimize the height of the tree.
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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.