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Python Coding
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467 challenges 330 easy 120 medium 17 hard

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All Python Basics Strings & Text Lists & Arrays Dicts & Sets Functions & Closures OOP & Classes Data Structures & Algorithms Advanced Python Iterators & Generators Decorators & Context Managers Error Handling & Exceptions Regular Expressions Math & Number Theory Bit Manipulation Dynamic Programming Trees & Binary Trees Graphs & Graph Algorithms Recursion & Backtracking Greedy Algorithms Binary Search Two Pointers & Sliding Window Stacks & Queues Heaps & Priority Queues Linked Lists Matrix & 2D Arrays Datetime & Time Calculations Data Formats & Parsing SQL & SQLite Numpy & Vectorized Computing Cryptography & Hashing

Lists & Arrays easy

Remove duplicates (sorted)

Return a sorted list with duplicates removed.

arrays two-pointer

Lists & Arrays easy

All Unique Values Keep Order

Remove duplicates from a list, keeping only the first occurrence of each value while preserving relative order.

deduplicate order list

Lists & Arrays easy

Is Subset of Another List

Write a function that returns True if every element in a given list exists in another list, ignoring duplicates.

subset membership lists

Lists & Arrays medium

Find Duplicate Number

Given a list of n+1 integers in the range 1..n, find the one integer that appears more than once.

arrays hash-set duplicates

Lists & Arrays easy

Difference of Two Lists

Write a function that returns items in list a that are not in list b, preserving order and duplicates.

lists difference counting

Showing 5 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.