Remove Duplicates from Sorted Array
Given a sorted list, remove duplicates in-place and return the new length.
Remove Duplicates from String
Given a string, return a new string with each character that repeats consecutively reduced to a single occurrence.
Remove duplicates (sorted)
Return a sorted list with duplicates removed.
All Unique Values Keep Order
Remove duplicates from a list, keeping only the first occurrence of each value while preserving relative order.
Is Subset of Another List
Write a function that returns True if every element in a given list exists in another list, ignoring duplicates.
Find Duplicate Number
Given a list of n+1 integers in the range 1..n, find the one integer that appears more than once.
Difference of Two Lists
Write a function that returns items in list a that are not in list b, preserving order and duplicates.
Pair with difference K
Count unordered index pairs with absolute difference exactly K, handling duplicates correctly.
Delete duplicates sorted II
Given a sorted list, remove duplicates in place so each element appears at most twice, returning the new length.
Permutations II
Return all distinct permutations of a list of integers that may include duplicates.
Subsets II
Given a collection of integers that might contain duplicates, return all possible unique subsets.
Rotated Array Search II
Implement a function to search for a target in a rotated sorted array with possible duplicates.
Showing 1–12 of 12 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.