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467 challenges 330 easy 120 medium 17 hard

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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

Iterators & Generators easy

Tree inorder generator

Write a generator function that yields a binary tree's node values in inorder traversal.

generator inorder binary-tree

Trees & Binary Trees easy

Binary Tree Inorder Traversal

Implement an inorder traversal function that returns node values in left-root-right order.

binary-tree traversal recursion

Trees & Binary Trees easy

Preorder Traversal

Implement a function that returns the preorder traversal values of a binary tree.

binary-tree traversal recursion

Trees & Binary Trees easy

Postorder Traversal

Implement a function that returns the postorder traversal of a binary tree as a list of node values.

binary-tree traversal recursion

Trees & Binary Trees easy

Maximum depth of tree

Implement max_depth(root) to return the maximum depth of a binary tree.

binary-tree recursion depth

Trees & Binary Trees easy

Minimum Depth of Tree

Given a binary tree, compute the minimum depth from the root to the nearest leaf node.

binary-tree depth traversal

Trees & Binary Trees easy

Symmetric Tree Check

Write a function that checks whether a binary tree is symmetric (a mirror of itself).

binary-tree recursion mirror

Trees & Binary Trees easy

Same Tree Check

Write a function that checks whether two binary trees are identical in structure and node values.

binary tree recursion tree traversal

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

Showing 13 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.