Middle Element of an Odd-Length List
Implement a function that returns the middle element of an odd-length list.
Is Subset of Another List
Write a function that returns True if every element in a given list exists in another list, ignoring duplicates.
Unzip pairs into two lists
Write a function that takes a list of pairs and returns two separate lists: first elements and second elements.
Generate a Multiplication Table
Build a function that returns an n x n multiplication table as a list of lists.
Find Second Largest
Find the second largest unique number in a list, or None if it doesn't exist.
Move Zeros to End
Rearrange a list by moving all zeros to the end while preserving the relative order of non-zero elements.
Majority Element Finder
Implement a function that returns the majority element in a list, which appears more than half the time.
Find Duplicate Number
Given a list of n+1 integers in the range 1..n, find the one integer that appears more than once.
Intersection of Two Lists
Given two lists, return a sorted list of unique elements that appear in both lists.
Union of Two Lists
Implement a function that combines two lists and returns only unique elements.
Difference of Two Lists
Write a function that returns items in list a that are not in list b, preserving order and duplicates.
Chunk list into groups
Implement a function that splits a list into sublists of a given size.
Zip Two Lists
Write a function that pairs elements from two lists by index, stopping at the shorter list.
Partition Array
Implement a function that finds a contiguous partition of a list into k groups, minimizing the maximum sum of the groups.
Rearrange Positives and Negatives
Write a function that rearranges a list in-place so all negative numbers come before non-negative numbers.
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.
Two Missing Numbers
Given a list of n-2 unique integers from 1 to n, find the two missing numbers efficiently.
Three Missing Numbers
Find the three missing numbers from a shuffled list containing all but three integers from 1 to n.
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.
Count Smaller Numbers
Given an integer list, return for each position how many later elements are smaller than it.
Move Zeroes
Implement move_zeroes(nums) that in-place moves all zeros to the end while maintaining the order of non-zero elements.
Showing 241–264 of 925 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.