Wave sort array
Given a list of integers, reorder it into a wave pattern where elements alternate down-up, and return the new list.
Last occurrence index
Implement a function that returns the last index of a given value in a list, or -1 if the value is not present.
Counting Sort
Implement the counting sort algorithm to sort a list of non-negative integers in O(n + k) time.
Image channel swap
Implement a function that swaps the red and blue channels of an RGB image.
Pad Array Edges
Write a function that pads a list with zeros on both ends.
Sort array by parity
Given a list of integers, return a new list with all evens first and odds last, preserving original relative order.
Count Adjacent Pairs
Given a list of integers and a target, count adjacent pairs whose sum equals the target.
Cartesian Product Pairs
Create a function that returns the Cartesian product of two lists as a sorted list of lists.
Reorder list halves
Implement reorder_list(nums) that returns the first half followed by the reversed second half.
Sort List Merge Sort
Write a function that sorts a list of integers using the merge sort algorithm.
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.
Insertion Sort
Implement insertion sort that sorts a list in-place and returns the same list.
Intersection two lists length
Return the number of distinct elements that appear in both input lists.
Running Total Window
Implement a function that returns a list of running totals, resetting to zero after each positive sum.
Normalize Array to Zero-One Range
Implement a function that normalizes a list of numbers to the range [0,1] using min-max scaling.
Boolean Mask Filter
Write a function that filters a list using a boolean mask and returns the matching elements as a list.
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.
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.
Showing 73–96 of 186 challenges · easy
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.