BFS level-order traversal
Return the level-order traversal of a binary tree as a list of lists.
Topological sort (Kahn)
Return a valid topological ordering of tasks, or [] if a cycle exists.
Word ladder length
Return the length of the shortest transformation from beginWord to endWord changing one letter at a time.
Shortest Path in Binary Matrix
Implement BFS to find the shortest path length from (0,0) to (n-1,n-1) in an n x n binary matrix, moving through 0 cells in 8 directions.
Flood Fill Algorithm
Implement flood fill on a 2D grid using BFS/DFS.
Level Order Traversal
Implement a function that performs a level order traversal of a binary tree and returns node values as a list of lists.
Binary tree left side view
Given a binary tree, return the leftmost node's value at each depth, from top to bottom.
Vertical Order Traversal
Compute the vertical order traversal of a binary tree, grouping nodes by column and row.
Minimum Cut
Given an undirected graph in adjacency-list form, return the size of the minimum edge cut that disconnects the graph.
Bipartite Graph Check
Implement a function to check if an undirected graph is bipartite using graph coloring.
Graph Coloring
Given an undirected graph, determine if it can be colored with two colors such that adjacent vertices have different colors.
Course Schedule Can Finish
Given numCourses and prerequisites, return whether all courses can be finished without cyclic dependencies.
Graph Valid Tree
Determine if n nodes and an edge list form a valid tree (connected and acyclic).
Cheapest Flights Within K Stops
Implement a function to compute the cheapest flight price from source to destination with at most K stops in a directed weighted graph.
Keys and Rooms
A classic graph traversal challenge: check if all rooms are reachable from room 0 using keys found in visited rooms.
Swim in Rising Water
Find the minimum time needed to swim from the top-left to the bottom-right of a grid where water level rises and you can only move to cells with elevation ≤ current time.
Surrounded Regions
Given an M×N grid of 'X' and 'O', capture all regions of 'O' that are completely surrounded by 'X'.
Course Schedule Ordering
Determine a valid sequence to complete all courses respecting prerequisite constraints.
Minimum Height Trees
Given an undirected tree, find all root nodes that minimize the height of the tree.
Open the Lock BFS
Implement a BFS solution to find the minimum number of turns needed to open a 4-wheel lock, avoiding a set of deadends.
Minimum Genetic Mutation
Implement a function to compute the minimum number of single-character mutations needed to transform one gene string into another, using a given bank of valid mutations.
Possible bipartition
Given N people and a list of mutual dislikes, check if they can be divided into two groups with no dislike inside a group.
Jump Game on Graph
Implement a function that determines if you can reach the last node of a directed graph by jumping from node 0 to node n-1 using edges.
Remove invalid parentheses
Given a string with parentheses and letters, return all valid strings after removing the minimum number of invalid parentheses.
Showing 1–24 of 30 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.