feat: add Morris Inorder Traversal algorithm in JavaScript issue #1806

Trees/MorrisTraversal.js

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+// Morris Inorder Traversal
+// Reference: https://www.geeksforgeeks.org/dsa/inorder-tree-traversal-without-recursion-and-without-stack/
+
+/*
+ * Author: Saad Arqam
+ * Morris Inorder Traversal Algorithm implementation in JavaScript
+ *
+ * Morris Traversal is a tree traversal algorithm that allows
+ * inorder traversal without using recursion or a stack.
+ * It achieves O(1) extra space by temporarily modifying
+ * the tree structure (creating and removing "threads").
+ *
+ * Reference:
+ * https://en.wikipedia.org/wiki/Threaded_binary_tree#Morris_traversal
+ */
+
+
+
+// Node class
+export class Node {
+  constructor(val) {
+    this.val = val
+    this.left = null
+    this.right = null
+  }
+}
+
+// Morris Inorder Traversal function
+export function morrisTraversal(node) {
+  const result = []
+  let curr = node
+
+  while (curr !== null) {
+    if (curr.left === null) {
+      result.push(curr.val)
+      curr = curr.right
+    } else {
+      let predecessor = curr.left
+      while (predecessor.right !== null && predecessor.right !== curr) {
+        predecessor = predecessor.right
+      }
+      if (predecessor.right === null) {
+        predecessor.right = curr
+        curr = curr.left
+      } else {
+        predecessor.right = null
+        result.push(curr.val)
+        curr = curr.right
+      }
+    }
+  }
+
+  return result
+}
+
+
+
+
+// Example Tree:
+//     7
+//    / \
+//   5   8
+//  / \
+// 3   6
+//      \
+//       9
+//
+// Morris inorder traversal: [3, 5, 6, 9, 7, 8]
+
+

Trees/MorrisTraversal.test.js

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+import { describe, it, expect } from 'vitest'
+import { Node, morrisTraversal } from './MorrisTraversal.js'
+
+describe('Morris Inorder Traversal', () => {
+  it('should return inorder traversal for a binary tree', () => {
+    // Tree:
+    //      4
+    //     / \
+    //    2   5
+    //   / \
+    //  1   3
+    const root = new Node(4)
+    root.left = new Node(2)
+    root.right = new Node(5)
+    root.left.left = new Node(1)
+    root.left.right = new Node(3)
+
+    const result = morrisTraversal(root)
+    expect(result).toEqual([1, 2, 3, 4, 5])
+  })
+
+  it('should return empty array for null input', () => {
+    const result = morrisTraversal(null)
+    expect(result).toEqual([])
+  })
+
+  it('should handle larger tree', () => {
+    // Tree:
+    //      7
+    //     / \
+    //    5   8
+    //   / \
+    //  3   6
+    //       \
+    //        9
+    const root = new Node(7)
+    root.left = new Node(5)
+    root.right = new Node(8)
+    root.left.left = new Node(3)
+    root.left.right = new Node(6)
+    root.left.right.right = new Node(9)
+
+    const result = morrisTraversal(root)
+    expect(result).toEqual([3, 5, 6, 9, 7, 8])
+  })
+})