[FEATURE]: Add Kahn's Algorithm in Graphs #1795

Author: Virus2hell

Graphs/__tests__/KahnsAlgorithm.test.js

@@ -0,0 +1,29 @@
+const { kahnTopologicalSort } = require('../KahnsAlgorithm');
+
+describe("Kahn's Algorithm", () => {
+  test('DAG returns valid topological order', () => {
+    const V = 6;
+    const edges = [[5,2],[5,0],[4,0],[4,1],[2,3],[3,1]];
+    const order = kahnTopologicalSort(V, edges);
+    expect(order.length).toBe(V);
+    const pos = Array(V);
+    for (let i = 0; i < order.length; i++) pos[order[i]] = i;
+    for (const [u,v] of edges) expect(pos[u]).toBeLessThan(pos[v]);
+  });
+
+  test('Cycle returns empty array', () => {
+    const V = 3;
+    const edges = [[0,1],[1,2],[2,0]];
+    expect(kahnTopologicalSort(V, edges)).toEqual([]);
+  });
+
+  test('Includes isolated nodes', () => {
+    const V = 4;
+    const edges = [[0,1],[2,3]];
+    const order = kahnTopologicalSort(V, edges);
+    expect(order.length).toBe(V);
+    const pos = Array(V);
+    for (let i = 0; i < order.length; i++) pos[order[i]] = i;
+    for (const [u,v] of edges) expect(pos[u]).toBeLessThan(pos[v]);
+  });
+});