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925 challenges 556 easy 323 medium 46 hard

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Lists & Arrays medium

Count Smaller Numbers

Given an integer list, return for each position how many later elements are smaller than it.

arrays counting merge-sort

Lists & Arrays easy

Sort array by parity

Given a list of integers, return a new list with all evens first and odds last, preserving original relative order.

sorting arrays two-pointers

Lists & Arrays easy

Cartesian Product Pairs

Create a function that returns the Cartesian product of two lists as a sorted list of lists.

lists tuples sorting

Lists & Arrays easy

Reorder list halves

Implement reorder_list(nums) that returns the first half followed by the reversed second half.

lists slicing reversal

Lists & Arrays easy

Convert Binary Number List

Given a list of bits (0s and 1s) in most-significant-first order, return the equivalent integer value.

binary lists conversion

Lists & Arrays easy

Insertion Sort

Implement insertion sort that sorts a list in-place and returns the same list.

sorting in-place algorithms

Lists & Arrays easy

Intersection two lists length

Return the number of distinct elements that appear in both input lists.

lists sets intersection

Lists & Arrays easy

Running Total Window

Implement a function that returns a list of running totals, resetting to zero after each positive sum.

running-total sliding-window arrays

Lists & Arrays easy

Boolean Mask Filter

Write a function that filters a list using a boolean mask and returns the matching elements as a list.

mask filter list

Lists & Arrays easy

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.

sliding-window lists averaging

Lists & Arrays easy

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.

lists encoding matrices

Lists & Arrays easy

Average Salary by Department

Given a list of employee tuples (name, department, salary), return a dictionary mapping each department to its average salary.

averages dictionaries lists

Showing 25–36 of 36 challenges · Lists & Arrays

Lists & Arrays — Python coding challenges

What you will find here

This page lists lists & arrays challenges — real Python problems you solve in the browser IDE with instant test feedback. Each challenge includes a clear brief, starter code, and automated checks.

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.