Additive number sequence
Check whether a given digit string can be partitioned into a valid additive sequence where each term is the sum of the previous two.
Path Sum II All Paths
Return all root-to-leaf paths where the sum of node values equals a target.
Reconstruct Itinerary
Given a list of airline tickets, reconstruct the itinerary in order using each ticket exactly once, choosing the lexicographically smallest path when multiple options exist.
Matchsticks to Square
Given a list of matchstick lengths, decide if they can form a square by using each matchstick exactly once.
Shortest Common Supersequence
Given two strings, return any shortest supersequence that contains both as subsequences.
Hamiltonian Path Check
Implement a function that checks whether an undirected graph has a Hamiltonian path using DFS and backtracking.
All Paths from Source to Target
Given a directed acyclic graph, return all paths from node 0 to the last node.
Graph Coloring Backtrack
Given an adjacency list and a number of colors, decide if the graph can be colored so no adjacent vertices share a color.
Android unlock patterns
Count the number of valid Android unlock patterns of a given length using a 3x3 grid with adjacency constraints.
Combination Generator
Write a recursive function that returns all combinations of length k from a list of distinct integers.
Generate Parentheses
Given n, generate all valid strings of n pairs of parentheses.
Letter Combinations of a Phone Number
Given a string of digits, return all possible letter combinations that the number could represent on a phone keypad.
Permutations II
Return all distinct permutations of a list of integers that may include duplicates.
Subsets
Return all subsets (the power set) of a list of distinct integers.
Subsets II
Given a collection of integers that might contain duplicates, return all possible unique subsets.
N-Queens Count
Count the number of distinct valid placements of n non-attacking queens on an n×n chessboard.
Word Search Backtrack
Determine if a given word exists in a 2D board by tracing adjacent cells without reusing any cell.
Palindrome Partitioning
Given a string s, return all possible palindrome partitioning of s.
Partition Equal Subset Sum (Backtracking)
Write a function that uses backtracking to decide if a list of positive integers can be partitioned into two subsets with equal sum.
Letter Tile Possibilities
Given a string of letter tiles, count the number of distinct non-empty sequences that can be formed using any non-empty subset in any order.
Combination Sum
Given a list of distinct positive integers and a target, return all unique combinations that sum to the target.
Beautiful Arrangement Count
Count the number of permutations of 1..n such that for every index i, either i is divisible by the number at that position or the number is divisible by i.
Rat in a Maze
Count the number of distinct paths a rat can take from top-left to bottom-right in a binary grid, moving down or right and avoiding walls.
Showing 1–23 of 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.