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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

Python Basics medium

Fibonacci(n)

Return the nth Fibonacci number efficiently.

recursion dp memoization

Lists & Arrays medium

Flatten nested list

Yield every integer from an arbitrarily nested list, depth-first.

recursion generators

Dicts & Sets medium

Hash map merge

Write a function that merges two dictionaries recursively, combining values and preserving structure.

dictionaries recursion merging

Data Structures & Algorithms medium

Quicksort

Implement quicksort and return a sorted list.

sorting recursion divide-and-conquer

Data Structures & Algorithms medium

Graph DFS

Return all nodes reachable from a start node via DFS.

graph DFS recursion

Data Structures & Algorithms medium

Merge Sort

Implement merge_sort(numbers) that returns a sorted copy of the input list using the merge sort algorithm.

sorting recursion divide-and-conquer

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

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

Recursion & Backtracking medium

Combination Generator

Write a recursive function that returns all combinations of length k from a list of distinct integers.

recursion backtracking combinations

Showing 11 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.