Graph DFS
Return all nodes reachable from a start node via DFS.
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.
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.
Eulerian Path Check
Given the number of vertices and an edge list of an undirected graph, decide if it has an Eulerian path.
Accounts Merge
Given a list of accounts, merge those that share any email and return sorted accounts.
Bellman-Ford Algorithm
Implement the Bellman-Ford algorithm to compute shortest distances from a source in a directed weighted graph with up to 100 vertices and negative edges.
Articulation Points
Implement a function that returns the articulation points of an undirected graph.
Bridges in Graph
Implement a function that returns all bridges in an undirected graph.
Hamiltonian Path Check
Implement a function that checks whether an undirected graph has a Hamiltonian path using DFS and backtracking.
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.
Alien Dictionary Order
Given a sorted list of words in an alien language, derive the order of its unique letters.
Graph Valid Tree
Determine if n nodes and an edge list form a valid tree (connected and acyclic).
All Paths from Source to Target
Given a directed acyclic graph, return all paths from node 0 to the last node.
Network Delay Time
Given a directed weighted graph and a starting node, find the minimum time for a signal to reach all nodes, or -1 if unreachable.
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.
Prim's Minimum Spanning Tree
Given a connected undirected weighted graph, compute the total weight of its minimum spanning tree using Prim's algorithm.
Kruskal MST
Implement Kruskal's algorithm to compute the total weight of a minimum spanning tree in a connected undirected graph.
Topological Sort via DFS
Return a deterministic topological ordering of nodes in a directed acyclic graph using DFS, or an empty list if a cycle exists.
Strongly Connected Components (Kosaraju's Algorithm)
Implement a function to find strongly connected components in a directed graph using Kosaraju's algorithm.
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.
Showing 1–24 of 34 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.