Reverse Pairs Count
Implement a function to count reverse pairs in an array efficiently.
Two Sum Sorted
Given a 1-indexed sorted array and a target, return the two indices that add up to the target.
Closest Three Sum
Given an array of integers and a target, return the sum of three numbers that is closest to the target.
Squares of Sorted Array
Implement a function that returns a sorted list of squares for a given non-decreasing integer array.
Interval List Intersections
Given two lists of sorted, disjoint intervals, return the list of intersections between them.
Minimum Size Subarray Sum
Given an array of positive integers, return the minimal length of a contiguous subarray with sum at least target, or 0 if none exists.
Fruit into Baskets
Given an array of integers representing fruit types, return the maximum number of fruits you can collect in a contiguous subarray with at most two distinct types.
Binary Subarray with Sum
Given a binary list and a goal sum, count the number of subarrays that add up to that goal.
Subarray product less than K
Count contiguous subarrays where the product of all elements is strictly less than a target K.
Boats to Save People – Two Pointer
Implement a function that returns the minimum number of boats needed to rescue everyone, given a weight limit and each boat carrying at most two people.
Container With Most Water
Compute the maximum area between two vertical lines in an array of heights.
Trapping Rain Water (Two Pointers)
Given an array of non-negative integers representing elevation heights, compute how much water can be trapped after rain.
Four Sum
Find all unique quadruplets in an array that sum to a given target.
Longest Repeating Character Replacement
Given a string and an integer k, return the length of the longest substring that can be made of identical characters after at most k replacements.
Count Nice Subarrays
Count subarrays that contain exactly k odd numbers.
Count nodes in a linked list
Return how many values appear in the list (one per node).
Read the head node value
Return the first value or None when the list is empty.
Read the tail node value
Return the last value or None when the list is empty.
Reverse a linked list copy
Return a new list with node values in reverse order without mutating the input.
Concatenate two linked lists
Append the second list's nodes after the first and return a new list.
Value at index n
Return the value at zero-based index n or None if out of range.
Middle node index
Return the floor middle index for a non-empty list.
Sum all node values
Add every integer payload in the list.
Maximum node value
Return the largest integer or None when empty.
Showing 25–48 of 64 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.