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Python Coding
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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

Data Structures & Algorithms medium

Path Sum II All Paths

Return all root-to-leaf paths where the sum of node values equals a target.

binary-tree dfs backtracking

Data Structures & Algorithms medium

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.

graphs union-find cycle-detection

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

Delete Node in BST

Implement a function that deletes a key from a binary search tree and returns the new root.

binary-search-tree tree-traversal recursion

Trees & Binary Trees medium

Trim BST to range

Implement a function to trim a BST to only retain nodes with values in a given inclusive range.

bst recursion tree-pruning

Graphs & Graph Algorithms medium

Graph Valid Tree

Determine if n nodes and an edge list form a valid tree (connected and acyclic).

Showing 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.