Append a new tail
Add value after the last node.
Palindrome linked values
Check whether values read the same forwards and backwards.
Rotate list left by k
Move the first k nodes to the end (k may exceed length; use modulo).
Merge two sorted lists
Merge two ascending integer lists into one sorted list.
Remove duplicate values
Keep first occurrence of each value while preserving order.
Pairwise sum of adjacent nodes
Sum each adjacent pair; keep a lone last node as-is.
Count nodes equal to target
Count how many times target appears in the list.
Zip two linked lists
Interleave values from a and b until both are exhausted.
Split list at index
Return prefix and suffix tuples at index k.
Second node value
Return the second value or None if fewer than two nodes.
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 ''.
Insert value at index
Insert x at index i in a new list.
Compare two linked lists
Return True when both lists have identical values in order.
Matrix Multiply 2D
Write a function that multiplies two 2D matrices (lists of lists) and returns the product matrix.
Transpose 2D Array
Implement a function that returns the transpose of a rectangular 2D list.
Flatten nested JSON
Write a function that flattens nested JSON objects into a flat dictionary with dot-separated keys, handling lists and empty objects.
Inner Join Two Tables
Write a function that inner joins two lists of dictionaries on a common key and returns the combined rows.
Select All Users
Write a function that connects to an in-memory SQLite database and returns all users as a list of lists.
Element-wise vector addition
Add equal-length numeric lists element-wise.
Showing 97–116 of 116 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.