Count Smaller Numbers
Given an integer list, return for each position how many later elements are smaller than it.
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.
Running Total Window
Implement a function that returns a list of running totals, resetting to zero after each positive sum.
Normalize Array to Zero-One Range
Implement a function that normalizes a list of numbers to the range [0,1] using min-max scaling.
Rolling Window Mean
Given a list of numbers and a window size k, return a list of the means of every contiguous subarray of length k.
Linear Interpolation Array
Given an array with some None values, replace them by linear interpolation between the nearest known values.
Convolve 1D Signal
Write a function that computes the 1D convolution of two lists in 'full' mode.
Pad array edges
Implement a function that pads a list on both ends with a given value to a specified total length.
Subarray sum equals K
Count the number of contiguous subarrays whose sum equals k.
Longest Harmonious Subsequence
Given a list of integers, find the length of the longest harmonious subsequence where the difference between maximum and minimum values is exactly 1.
Index of peak element
Implement a function that returns the index of any peak element in a given integer array.
Count pairs with given difference
Count how many unordered pairs in a list have a given absolute difference using an efficient approach.
Find Peak Element
Implement a function that returns the index of any peak element in an integer array.
Previous Smaller Element
Find the nearest previous index with a smaller value for every element in an array.
Longest Consecutive Sequence
Given an unsorted list of integers, find the length of the longest consecutive elements sequence in O(n) time.
Median of Two Sorted Arrays
Given two sorted arrays, return the median of the combined sorted array in O(log(min(n,m))) time.
Pascal Triangle Row
Given a non-negative integer n, return the nth row of Pascal's triangle as a list of integers.
Bubble Sort
Implement bubble sort that sorts a list of numbers in ascending order.
Exponential Search
Implement exponential search to find any valid index of a target in a sorted list.
Find Peak Index
Given a list of integers, return the index of any peak element where the value is not smaller than its neighbors.
Peak Element in Array
Implement a function that returns the index of any peak element in a list of integers.
Count of Range Sum
Count contiguous subarrays whose sum lies in a given inclusive range using an efficient divide-and-conquer algorithm.
Showing 25–48 of 170 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.