Remove invalid parentheses
Given a string with parentheses and letters, return all valid strings after removing the minimum number of invalid parentheses.
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.
Hamiltonian Cycle Backtrack
Implement a backtracking algorithm to find a Hamiltonian cycle in an undirected graph.
Showing 25–31 of 31 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.