Partition around a pivot value
Implement an in-place partition of a list around a given pivot value, returning the boundary index.
Convolve 1D Signal
Write a function that computes the 1D convolution of two lists in 'full' mode.
BFS level-order traversal
Return the level-order traversal of a binary tree as a list of lists.
Top N per group
Implement top_n_per_group that returns the top N scores for each group from a list of (group, score) pairs.
Level Order Traversal
Implement a function that performs a level order traversal of a binary tree and returns node values as a list of lists.
Correlation Coefficient
Write a pure-Python function that computes the Pearson correlation coefficient between two lists of numbers.
Combination Generator
Write a recursive function that returns all combinations of length k from a list of distinct integers.
Queue Reconstruction by Height
Given shuffled pairs of (height, number_of_taller_people_in_front), reconstruct the original queue order.
Find k Closest Elements to Target
Return exactly k elements from a sorted list that are closest to a given target, preserving order.
Interval List Intersections
Given two lists of sorted, disjoint intervals, return the list of intersections between them.
Prepend a new head
Insert value at the front of the list.
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.
Flatten nested JSON
Write a function that flattens nested JSON objects into a flat dictionary with dot-separated keys, handling lists and empty objects.
Showing 1–21 of 21 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.