Add Level Order Traversal algorithm with Vitest tests

Author: aniket866

Trees/LevelOrderTraversal.js

@@ -0,0 +1,35 @@
+/**
+ * Level Order Traversal of a Binary Tree (Breadth-First Traversal)
+ */
+
+export class Node {
+  constructor(value) {
+    this.value = value;
+    this.left = null;
+    this.right = null;
+  }
+}
+
+export function levelOrderTraversal(root) {
+  if (!root) return [];
+
+  const result = [];
+  const queue = [root];
+
+  while (queue.length > 0) {
+    const levelSize = queue.length;
+    const currentLevel = [];
+
+    for (let i = 0; i < levelSize; i++) {
+      const node = queue.shift();
+      currentLevel.push(node.value);
+
+      if (node.left) queue.push(node.left);
+      if (node.right) queue.push(node.right);
+    }
+
+    result.push(currentLevel);
+  }
+
+  return result;
+}

Trees/test/LevelOrderTraversal.test.js

@@ -0,0 +1,32 @@
+import { Node, levelOrderTraversal } from "../LevelOrderTraversal.js";
+
+describe("Level Order Traversal", () => {
+  test("should return empty array for empty tree", () => {
+    expect(levelOrderTraversal(null)).toEqual([]);
+  });
+
+  test("should return single node tree", () => {
+    const root = new Node(1);
+    expect(levelOrderTraversal(root)).toEqual([[1]]);
+  });
+
+  test("should return correct level order for complete tree", () => {
+    const root = new Node(1);
+    root.left = new Node(2);
+    root.right = new Node(3);
+    root.left.left = new Node(4);
+    root.left.right = new Node(5);
+    root.right.left = new Node(6);
+    root.right.right = new Node(7);
+
+    expect(levelOrderTraversal(root)).toEqual([[1], [2, 3], [4, 5, 6, 7]]);
+  });
+
+  test("should handle unbalanced tree", () => {
+    const root = new Node(1);
+    root.left = new Node(2);
+    root.left.left = new Node(3);
+
+    expect(levelOrderTraversal(root)).toEqual([[1], [2], [3]]);
+  });
+});