Insert New Row
Implement a function that inserts a new row into a 2D list at a specified index.
Fancy Index Select
Given a 2D matrix and a list of row indices, select those rows in order and return them as a new 2D list.
Argmax along axis
Write a function that returns index positions of the maximum values along rows or columns of a 2D list.
Zigzag string conversion
Encode a string in zigzag order across numRows rows, then read row by row.
Design Browser History
Implement a BrowserHistory class that supports visit, back, and forward navigation with step counts.
Minimum Number of Arrows to Burst Balloons
Given balloon intervals, find the minimum number of arrows to burst all balloons by merging overlaps.
Search 2D Matrix
Given a sorted 2D matrix with sorted rows and first element of each row greater than last of previous, find target efficiently.
Join node values with arrows
Format string node values as 'a -> b -> c'; empty list returns ''.
Valid Sudoku Board
Determine if a 9x9 Sudoku board is valid by checking rows, columns, and 3x3 sub-boxes.
Valid Sudoku Validator
Determine if a given 9x9 Sudoku board is valid by checking rows, columns, and 3x3 boxes.
Update Row by ID
Given a list of CSV rows and target ID, replace the first matching row's value.
Parse table rows
Implement a function that converts a simple text table into a list of dictionaries.
Inner Join Two Tables
Write a function that inner joins two lists of dictionaries on a common key and returns the combined rows.
Index Creation Query
Create an in-memory SQLite database, execute CREATE INDEX statements, and return the resulting index metadata rows.
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.
Sum each matrix row
Given rows, return each row sum.
Flatten matrix to vector
Read rows left-to-right, top-to-bottom.
Transpose a matrix
Swap rows and columns for a rectangular matrix.
Showing 1–18 of 18 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.