Dot Product of Vectors
Implement a function that returns the dot product of two numeric vectors.
Modular Inverse
Implement a function that returns the modular inverse of a modulo m, or -1 if it does not exist.
Extended Euclidean Algorithm
Implement the extended Euclidean algorithm to return (gcd, x, y) such that ax + by = gcd(a, b).
Deficient Number Check
Write is_deficient(n) that returns True if the sum of proper divisors is less than n.
Kaprekar number check
Check whether a given non-negative integer is a Kaprekar number in base 10.
Stars and Bars Count
Implement stars_and_bars_count(n, k) which returns the number of ways to put n identical items into k distinct bins, with bins allowed to be empty.
Multinomial coefficient
Write a function to compute the multinomial coefficient efficiently for given nonnegative counts.
Correlation Coefficient
Write a pure-Python function that computes the Pearson correlation coefficient between two lists of numbers.
Z score normalization
Compute the z-scores for a list of numbers using the population standard deviation.
Missing Number XOR
Given a list of n distinct numbers from 0 to n with one missing, use XOR to find and return the missing number.
Bell number
Implement a function to compute the Bell number B(n) using dynamic programming.
Perfect Squares Sum
Given a positive integer n, return the least number of perfect squares (e.g., 1, 4, 9, 16, ...) that sum to n.
Integer Break Product
Given a positive integer n, break it into at least two positive integers that sum to n and maximize their product.
Ugly Number II
Given an integer n, return the nth ugly number using an efficient dynamic programming approach.
Derangement count
Implement a function to count derangements of n items using the classic recurrence.
Tiling dominoes count
Given a 2 x n board, count the distinct tilings using 2 x 1 dominoes.
Kth Missing Positive
Given a strictly increasing array and an integer k, return the k-th positive integer that is missing from the array.
Minimum Speed to Arrive on Time
Given commute distances and a time limit, compute the minimum integer speed so you arrive on time.
Nth Magical Number
Given three integers n, a, b, return the nth positive integer that is divisible by either a or b.
Maximum Average Pass Ratio
Given class pass/total counts and extra students, maximize the average pass ratio by assigning extra students optimally.
Days in month
Write a function that returns the number of days in a given month and year, correctly handling leap years.
Showing 49–69 of 69 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.