Practice Arena

Python Coding
Challenges

Write real Python in the browser. Instant feedback. From beginner to expert.

925 challenges 556 easy 323 medium 46 hard

All Easy Medium Hard

All Python Basics Strings & Text Lists & Arrays Dicts & Sets Functions & Closures OOP & Classes Data Structures & Algorithms Advanced Python Iterators & Generators Decorators & Context Managers Error Handling & Exceptions Regular Expressions Math & Number Theory Bit Manipulation Dynamic Programming Trees & Binary Trees Graphs & Graph Algorithms Recursion & Backtracking Greedy Algorithms Binary Search Two Pointers & Sliding Window Stacks & Queues Heaps & Priority Queues Linked Lists Matrix & 2D Arrays Datetime & Time Calculations Data Formats & Parsing SQL & SQLite Numpy & Vectorized Computing Cryptography & Hashing

Data Structures & Algorithms medium

BFS level-order traversal

Return the level-order traversal of a binary tree as a list of lists.

BFS trees queues

Data Structures & Algorithms medium

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.

binary-tree queue bfs

Trees & Binary Trees medium

Lowest Common Ancestor in a Binary Tree

Implement a function to find the lowest common ancestor (LCA) of two nodes in a binary tree.

binary-tree dfs recursion

Trees & Binary Trees medium

Sum Root to Leaf Numbers

Given the root of a binary tree, compute the total sum of all root-to-leaf numbers.

binary-tree dfs recursion

Trees & Binary Trees medium

Binary tree left side view

Given a binary tree, return the leftmost node's value at each depth, from top to bottom.

binary-tree levels bfs

Trees & Binary Trees medium

Vertical Order Traversal

Compute the vertical order traversal of a binary tree, grouping nodes by column and row.

binary-tree bfs dictionary

Trees & Binary Trees medium

Validate BST

Implement a function to determine if a binary tree is a valid Binary Search Tree.

bst recursion validation

Trees & Binary Trees medium

Count Complete Tree Nodes

Given a complete binary tree, return its node count faster than O(n) time.

binary-tree complete-tree tree-traversal

Trees & Binary Trees medium

Zigzag Level Order Traversal

Implement a function that returns the zigzag level-order traversal of a binary tree.

binary-tree breadth-first-search queue

Trees & Binary Trees medium

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).

binary-tree breadth-first-search queue

Showing 1–10 of 10 challenges · medium

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.