Reorder list halves
Implement reorder_list(nums) that returns the first half followed by the reversed second half.
Rotate List Right by k
Implement a function that rotates a list to the right by k positions.
Convert Binary Number List
Given a list of bits (0s and 1s) in most-significant-first order, return the equivalent integer value.
Intersection two lists length
Return the number of distinct elements that appear in both input lists.
Flatten Multidimensional Lists
Write a function that flattens arbitrarily nested lists of integers into a single list.
Concatenate Horizontally
Write a function that horizontally concatenates two 2D lists into a new 2D list.
Rolling Window Mean
Given a list of numbers and a window size k, return a list of the means of every contiguous subarray of length k.
Linear Interpolation Array
Given an array with some None values, replace them by linear interpolation between the nearest known values.
One Hot Encode Labels
Given a list of categorical labels, return a list of one-hot encoded vectors based on the sort order of unique labels.
Convolve 1D Signal
Write a function that computes the 1D convolution of two lists in 'full' mode.
Average Salary by Department
Given a list of employee tuples (name, department, salary), return a dictionary mapping each department to its average salary.
Pad array edges
Implement a function that pads a list on both ends with a given value to a specified total length.
List intersection
Return the sorted list of elements common to both lists.
Are two lists the same multiset
Write a function that checks if two lists contain the same elements with the same multiplicities, ignoring order.
Sort by frequency
Sort a list by element frequency descending, with ties broken by order of first occurrence.
Set intersection size
Count how many distinct values appear in both of two given lists.
Symmetric Difference
Write a function that computes the symmetric difference of two lists, returning a sorted list of unique elements.
Disjoint Set Check
Check if two lists are disjoint by verifying they have no common elements.
Group by Department
Implement a function that groups a list of employee dictionaries by department, returning a dictionary keyed by department with lists of employee dictionaries.
BFS level-order traversal
Return the level-order traversal of a binary tree as a list of lists.
Selection Sort Implementation
Implement selection sort to sort a list of numbers in ascending order.
Merge Two Sorted Lists
Write a function that merges two sorted lists into a single sorted list.
Delete Old Records
Filter a list of records by removing those with a date older than a given cutoff date.
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.
Showing 49–72 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.