Remove Duplicates from Sorted Array
Given a sorted list, remove duplicates in-place and return the new length.
Palindrome check
Return True if the string reads the same forwards and backwards (ignoring case and non-alphanumeric).
Remove duplicates (sorted)
Return a sorted list with duplicates removed.
Merge two sorted arrays
Merge two sorted arrays into one sorted array.
Move Zeros to the End
Reorder a list in-place, pushing all zeros to the end while preserving the order of non-zero numbers.
Move Zeros to End
Rearrange a list by moving all zeros to the end while preserving the relative order of non-zero elements.
Rearrange Positives and Negatives
Write a function that rearranges a list in-place so all negative numbers come before non-negative numbers.
Move Zeroes
Implement move_zeroes(nums) that in-place moves all zeros to the end while maintaining the order of non-zero elements.
Sort array by parity
Given a list of integers, return a new list with all evens first and odds last, preserving original relative order.
Merge Sorted Array In Place
Write a function that merges two sorted arrays into the first array in-place, keeping the result sorted.
Shortest Unsorted Continuous Subarray
Given an array of integers, return the length of the shortest contiguous subarray whose sorting makes the whole array sorted.
Assign Cookies
Given child greed factors and cookie sizes, return the maximum number of content children.
Longest Substring Without Repeating Characters
Implement a function that returns the length of the longest substring without repeating characters.
Reduce array to zero
Given an array of non-negative integers, each operation chooses two indices and subtracts 1 from each if both are positive. Return the minimum number of operations to reduce the array to all zeros, or -1 if impossible.
Two Sum Sorted
Given a 1-indexed sorted array and a target, return the two indices that add up to the target.
Squares of Sorted Array
Implement a function that returns a sorted list of squares for a given non-decreasing integer array.
Container With Most Water
Compute the maximum area between two vertical lines in an array of heights.
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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.