Two Missing Numbers
Given a list of n-2 unique integers from 1 to n, find the two missing numbers efficiently.
Three Missing Numbers
Find the three missing numbers from a shuffled list containing all but three integers from 1 to n.
Count Smaller Numbers
Given an integer list, return for each position how many later elements are smaller than it.
Count inversions lite
Implement a function that counts inversions in a list of numbers efficiently.
Merge Sort
Implement merge_sort(numbers) that returns a sorted copy of the input list using the merge sort algorithm.
Bucket Sort
Implement bucket sort to sort a list of floating-point numbers in the range [0,1).
Strobogrammatic number II
Given a positive integer n, return all strobogrammatic numbers of length n in ascending order.
Multiprocessing Queue
Implement a function that uses a multiprocessing queue to compute factorials of a list of numbers in parallel.
Prime Sieve Generator
Implement a generator function that yields prime numbers from 2 up to a specified limit, using an efficient sieve approach.
Correlation Coefficient
Write a pure-Python function that computes the Pearson correlation coefficient between two lists of numbers.
Bitwise AND of a Range
Given a range [a, b], return the bitwise AND of all integers in that inclusive range without iterating over all numbers.
Maximum XOR Pair
Implement max_xor_pair(nums) that returns the maximum XOR value obtainable by pairing any two numbers in the given list.
Sum Root to Leaf Numbers
Given the root of a binary tree, compute the total sum of all root-to-leaf numbers.
Count Nice Subarrays
Given an array of integers, count the number of contiguous subarrays that contain exactly k odd numbers.
Closest Three Sum
Given an array of integers and a target, return the sum of three numbers that is closest to the target.
Count Nice Subarrays
Count subarrays that contain exactly k odd numbers.
Julian Day Number Converter
Implement two functions to convert between Gregorian calendar dates and Julian Day Numbers using a standard formula.
Extract JSON-like numbers
Parse a simplified JSON-like string without using the json module and sum all numbers found in it.
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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.