Fibonacci(n)
Return the nth Fibonacci number efficiently.
Run-length encoding
Compress consecutive identical characters, e.g. 'aaabbc' → 'a3b2c1'.
Longest common prefix
Find the longest common prefix among a list of strings.
Integer to Roman
Convert a positive integer to its Roman numeral representation.
Zigzag string conversion
Encode a string in zigzag order across numRows rows, then read row by row.
Maximum subarray (Kadane)
Find the contiguous subarray with the largest sum.
Rotate array
Rotate a list right by k positions in place.
Flatten nested list
Yield every integer from an arbitrarily nested list, depth-first.
Merge intervals
Merge all overlapping intervals and return a sorted result.
Product except self
Return an array where output[i] is the product of all elements except nums[i], without using division.
Group anagrams
Group words that are anagrams of each other.
Subarray sum equals K
Count the number of contiguous subarrays whose sum equals k.
Memoize decorator
Implement a @memoize decorator that caches results of a function.
Function composition
Return a function that applies f after g: compose(f, g)(x) == f(g(x)).
Linked list reversal
Implement a singly linked list and a function to reverse it in place.
Matrix addition operator
Implement a Matrix class that supports + and * operators.
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.
Coin change (DP)
Find the minimum number of coins to make exactly the target amount.
Graph DFS
Return all nodes reachable from a start node via DFS.
Context manager timer
Implement a Timer context manager that records elapsed seconds.
Retry decorator
Implement @retry(times=3) that retries a function on exception.
2D Vector dataclass
Implement a Vector2D dataclass with +, -, scalar *, dot product, and magnitude.
Showing 23 challenges · medium
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.