Count Nice Subarrays
Given an array of integers, count the number of contiguous subarrays that contain exactly k odd numbers.
Subarrays with K different ints
Count the number of contiguous subarrays that contain exactly K distinct integers.
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.
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.
Three Sum
Given an array of integers, return all unique triplets that sum to zero.
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.
Longest Substring with At Most K Distinct Characters
Given a string and an integer k, find the length of the longest substring that contains at most k distinct characters.
Minimum Window Subsequence
Given strings s and t, return the minimum window substring of s that contains t as a subsequence, or empty string if none exists.
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.
Sliding Window Median
Given a list of integers and a positive window size k, return the median of each sliding window of length k.
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.
Balanced brackets in string
Check if a string of brackets is properly balanced using a stack-based approach.
Next Greater Element
Return a list where each position holds the next greater element to the right, or -1 if none exists.
Showing 745–768 of 925 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.