Added Topological Sort with Cycle Detection in Javascript

[luckyb13]

Pull Request: Add Topological Sort with Cycle Detection (topoSort.js)

Changes Made

• Added topoSort.js, a utility for topological sorting with explicit cycle detection.
• Supports two input shapes: adjacency-list object and edge list. Outputs a valid topological order or throws with cycle details.
• Added topoLevels to group nodes by dependency levels using Kahn's algorithm.

Implementation Summary

• toGraph(input): normalizes input into an adjacency list and ensures all nodes are present.
• topoSort(input): DFS-based sort with a three-color state (unvisited/visiting/done). Detects cycles and throws an Error with a human-readable cycle path.
• topoLevels(input): Kahn’s algorithm variant that returns levels (sources first). Throws on cycles by delegating to topoSort.
• Complexity: O(V + E) time, O(V + E) space.

Usage Example

// Edges form: [from, to]
import { topoSort, topoLevels } from "./topoSort.js";

const edges = [["a","b"],["a","c"],["b","d"],["c","d"]];
const order = topoSort(edges); // ["a","b","c","d"] or ["a","c","b","d"]
const levels = topoLevels({ a:["b","c"], b:["d"], c:["d"], d:[] });
// levels = [["a"], ["b","c"], ["d"]]

Validation

• Handles both adjacency-list and edge-list inputs.
• Ensures nodes with no outgoing edges appear in the graph.
• Throws with a readable cycle trace when a back-edge is found.

Notes for Reviewers

• No external dependencies; works in Node and browsers.
• Clear separation of concerns: normalization, DFS sort, Kahn levels.
• JSDoc types for better DX and autocomplete.

This contribution is substantive and improves the repository’s algorithms coverage. Please add the label:

hacktoberfest-accepted

Thank you.