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.
Find the Town Judge
Given n people and a trust array, return the town judge or -1.
Find center of star graph
Write a function that finds the center node of a star graph from its list of edges in O(1) time.
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.
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.
Clique Detection
Given an undirected graph and a list of vertices, check if every pair of distinct vertices in the list is connected by an edge.
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.
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.
Floyd-Warshall: All-Pairs Shortest Paths
Implement the Floyd-Warshall algorithm to find all-pairs shortest path distances in a directed graph with possibly negative weights but no negative cycles.
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.
Most stones removed
Given stone coordinates on a grid, find the maximum number of stones that can be removed while every stone shares a row or column with another remaining stone.
Showing 25–48 of 53 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.