Practice Arena

Python Coding
Challenges

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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

Python Basics easy

Factorial (iterative)

Compute n! iteratively without recursion.

Python Basics easy

GCD via Euclid

Compute the greatest common divisor of two positive integers.

Python Basics medium

Fibonacci(n)

Return the nth Fibonacci number efficiently.

recursion dp memoization

Strings & Text hard

Basic Calculator III

Implement a recursive descent parser to evaluate a fully parenthesized arithmetic expression with +, -, *, / and parentheses.

parsing string expression

Lists & Arrays medium

Flatten nested list

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

recursion generators

Lists & Arrays easy

Sort List Merge Sort

Write a function that sorts a list of integers using the merge sort algorithm.

merge sort sorting recursion

Lists & Arrays easy

Flatten Multidimensional Lists

Write a function that flattens arbitrarily nested lists of integers into a single list.

recursion nested-lists flatten

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 easy

Employee Hierarchy

Build an employee hierarchy tree and compute the total number of direct and indirect reports for each employee.

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

Data Structures & Algorithms easy

Lowest Common Ancestor in a Binary Search Tree

Implement a function to find the lowest common ancestor of two node values in a binary search tree.

Data Structures & Algorithms hard

N-Queens Solutions

Implement a function to count the number of distinct ways to place n queens on an n×n board.

backtracking chess recursion

Data Structures & Algorithms medium

Strobogrammatic number II

Given a positive integer n, return all strobogrammatic numbers of length n in ascending order.

strings recursion number

Iterators & Generators easy

Graph DFS Generator

Implement a generator function that performs a depth-first traversal of a graph without recursion.

generators dfs graph

Math & Number Theory easy

Lucas Sequence

Implement a function to compute the n-th Lucas number using iteration or recursion with memoization.

math sequence dynamic programming

Math & Number Theory easy

Partition function

Write a function that returns the number of ways to write a positive integer as a sum of positive integers (order irrelevant).

math recursion memoization

Dynamic Programming easy

Derangement count

Implement a function to count derangements of n items using the classic recurrence.

dynamic-programming combinatorics recursion

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

Showing 1–24 of 57 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.