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925 challenges 556 easy 323 medium 46 hard

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Lists & Arrays easy

Running Product of Integers

Given a list of integers, return a new list where each element at index i is the product of all elements from index 0 to i.

prefix product lists

Lists & Arrays easy

Find Missing Number 1 to n

Given a list containing n-1 distinct integers from 1 to n, find the missing number without using extra space.

arrays math search

Lists & Arrays easy

Wave sort array

Given a list of integers, reorder it into a wave pattern where elements alternate down-up, and return the new list.

sorting swap rearrangement

Lists & Arrays easy

Counting Sort

Implement the counting sort algorithm to sort a list of non-negative integers in O(n + k) time.

sorting counting arrays

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

Count Adjacent Pairs

Given a list of integers and a target, count adjacent pairs whose sum equals the target.

pairs sum adjacent

Lists & Arrays easy

Sort List Merge Sort

Write a function that sorts a list of integers using the merge sort algorithm.

merge sort sorting recursion

Lists & Arrays easy

Flatten Multidimensional Lists

Write a function that flattens arbitrarily nested lists of integers into a single list.

recursion nested-lists flatten

Showing 1–8 of 8 challenges · easy · 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.