Remove the head node
Return a new list without the first node.
Drop the tail node
Return a new list without the last node.
Join node values with arrows
Format string node values as 'a -> b -> c'; empty list returns ''.
Count square submatrices with all ones
Count all square submatrices consisting entirely of 1s in a binary matrix.
Largest Plus Sign
Compute the largest possible plus sign of 1s in an n x n grid with some cells set to 0.
Word Search Matrix
Given a 2D board and a word, determine if the word can be formed by sequentially adjacent cells (horizontally or vertically), without reusing cells.
Age in years months days
Given birth and reference dates, return age as a dictionary with years, months, days.
Week Number ISO
Given a date, return its ISO 8601 week number (1–53) without using datetime.isocalendar().
Time Slot Generator
Generate a list of time slots of a specified duration within a start and end time.
Extract JSON-like numbers
Parse a simplified JSON-like string without using the json module and sum all numbers found in it.
Generate CSV row
Implement a function that converts a list of values into a single CSV row with correct quoting and escaping.
Parse YAML-like dict
Parse a simple YAML-like text with indentation into a nested dictionary.
Flatten nested JSON
Write a function that flattens nested JSON objects into a flat dictionary with dot-separated keys, handling lists and empty objects.
Unflatten JSON dict
Given a flat dictionary with keys like 'a.b.c', reconstruct the nested dictionary where each dotted segment becomes a nested level.
Encode Base64 String
Write a function that encodes a UTF-8 string into a base64 string without using the base64 module.
Serialize dict to TOML-like
Convert nested Python dicts into a simplified TOML-like string with sorted keys, type-aware formatting, and flat table sections.
Parse Apache log line
Write a function that parses a single Apache access log line into a dictionary with IP, timestamp, request, status, and size.
Create Table Schema
Write a function that creates a SQLite table with a given name and columns, and returns the resulting schema as a list of column definitions.
Customers Never Order
Given Customers and Orders tables, return the names of customers with no orders, sorted alphabetically, or None if all have ordered.
Add column alter
Write a function that connects to an in-memory SQLite database, creates a table, inserts rows, and adds a new column with ALTER TABLE.
Constant Time Compare
Write a function that compares two strings without leaking length or content via timing.
Password Salt Hash
Implement a function that returns a secure salted SHA-256 password hash with a deterministic format.
XOR Cipher Encode
Implement the XOR cipher: encode a string by XORing each character with a key character.
Showing 169–191 of 191 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.