Symmetric Difference
Write a function that computes the symmetric difference of two lists, returning a sorted list of unique elements.
Disjoint Set Check
Check if two lists are disjoint by verifying they have no common elements.
Frequency sort descending
Write a function that sorts a list by frequency descending while preserving original order for ties.
Count Pairs with Sum
Implement a function that counts the number of distinct pairs in a list summing to a target.
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.
Group by Department
Implement a function that groups a list of employee dictionaries by department, returning a dictionary keyed by department with lists of employee dictionaries.
Revenue by Month
Write a function that groups a list of (date, amount) pairs by year-month and returns total revenue per month as a sorted dictionary.
Linked list reversal
Implement a singly linked list and a function to reverse it in place.
Queue class (list-based)
Implement a Queue class with enqueue, dequeue, peek, is_empty, and is_full methods using a list.
Binary search
Return the index of target in a sorted list, or -1 if not present.
Quicksort
Implement quicksort and return a sorted list.
BFS level-order traversal
Return the level-order traversal of a binary tree as a list of lists.
Count inversions lite
Implement a function that counts inversions in a list of numbers efficiently.
Count pairs with given difference
Count how many unordered pairs in a list have a given absolute difference using an efficient approach.
Longest Consecutive Sequence
Given an unsorted list of integers, find the length of the longest consecutive elements sequence in O(n) 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.
Selection Sort Implementation
Implement selection sort to sort a list of numbers in ascending order.
Merge Sort
Implement merge_sort(numbers) that returns a sorted copy of the input list using the merge sort algorithm.
Heap Sort Implementation
Implement the heap sort algorithm to sort a list of comparable elements in non-decreasing order.
Radix Sort
Implement LSD radix sort to sort a list of non-negative integers in ascending order.
Bucket Sort
Implement bucket sort to sort a list of floating-point numbers in the range [0,1).
Exponential Search
Implement exponential search to find any valid index of a target in a sorted list.
Redundant Connection
Given a list of edges forming a tree plus one extra edge, return the edge that appears last in the input and creates a cycle.
Showing 121–144 of 273 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.