Sort array by parity
Given a list of integers, return a new list with all evens first and odds last, preserving original relative order.
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.
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.
Boolean Mask Filter
Write a function that filters a list using a boolean mask and returns the matching elements as a 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.
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.
Word frequency
Return a dict mapping each word to its count in the sentence.
List intersection
Return the sorted list of elements common to both lists.
Most frequent element
Return the element that appears most often in a list.
Word to Index Map
Create a function that returns a dictionary mapping each unique word to the index of its first occurrence.
Group names by first letter
Given a list of names, return a dictionary mapping each first letter to all names starting with that letter in original order.
Keys Sorted by Value Descending
Given a dictionary mapping strings to integers, return a list of keys sorted by value descending, and when values tie, alphabetically ascending.
Nested get with dotted path
Implement a function that safely retrieves a value from a deeply nested dictionary using a dot-separated path, returning a default if any key is missing.
Common Keys of Two Dictionaries
Implement a function that finds keys shared by two dictionaries and returns them sorted.
Union of Many Sets
Implement a function that takes any number of sets and returns a sorted list of their union.
Mode of a list via counting
Implement a function that returns the mode of a list, resolving ties by the element that appears first.
Top k keys by count
Given a dictionary mapping keys to counts, return the top k keys with the highest counts, breaking ties alphabetically.
Values that appear once
Return a list of numbers that appear exactly once in the input list, in original order.
Two Sum with Dict
Implement the classic Two Sum problem: return indices of two numbers that add up to a target using a dict.
Showing 121–144 of 371 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.