Tree Traversal Preorder Root Left Right in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start preorder traversal by visiting the root node first.

DSA Typescript

function preorder(node: TreeNode | null): void {
  if (node === null) return;
  console.log(node.val);
  preorder([1]);
}

Drag options to blanks, or click blank then click option'

Anode

Bnode.right

Cnode.left

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Calling preorder on right child first

Calling preorder on the node itself again causing infinite recursion

In preorder traversal, after visiting the root, we visit the left subtree first, so we call preorder on node.left.

2fill in blank

medium

Complete the code to continue preorder traversal by visiting the right subtree after the left.

DSA Typescript

function preorder(node: TreeNode | null): void {
  if (node === null) return;
  console.log(node.val);
  preorder(node.left);
  preorder([1]);
}

Drag options to blanks, or click blank then click option'

Anode.right

Bnode.left

Cnode

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Calling preorder on left child twice

Calling preorder on the node itself again

After visiting the root and left subtree, preorder traversal visits the right subtree, so we call preorder on node.right.

3fill in blank

hard

Fix the error in the preorder traversal function to avoid infinite recursion.

DSA Typescript

function preorder(node: TreeNode | null): void {
  if (node === null) return;
  console.log(node.val);
  preorder(node.left);
  preorder([1]);
}

Drag options to blanks, or click blank then click option'

Anode

Bnode.right

Cnull

Dnode.left

Attempts:

3 left

💡 Hint

Common Mistakes

Calling preorder on node itself

Calling preorder on null unnecessarily

Calling preorder on node again causes infinite recursion. We must call preorder on node.right to continue traversal correctly.

4fill in blank

hard

Fill both blanks to complete the preorder traversal function visiting root, left, then right.

DSA Typescript

function preorder(node: TreeNode | null): void {
  if (node === null) return;
  console.log(node.val);
  preorder([1]);
  preorder([2]);
}

Drag options to blanks, or click blank then click option'

Anode.left

Bnode.right

Cnode

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping left and right calls

Calling preorder on the node itself

Preorder traversal visits root first, then recursively visits left subtree (node.left), then right subtree (node.right).

5fill in blank

hard

Fill all three blanks to create a preorder traversal that prints the node value in uppercase, then visits left and right children.

DSA Typescript

function preorder(node: TreeNode | null): void {
  if (node === null) return;
  console.log(node.val[1]);
  preorder([2]);
  preorder([3]);
}

Drag options to blanks, or click blank then click option'

A.toUpperCase()

Bnode.left

Cnode.right

D.toLowerCase()

Attempts:

3 left

💡 Hint

Common Mistakes

Using .toLowerCase() instead of .toUpperCase()

Swapping left and right children calls

To print the node value in uppercase, use .toUpperCase(). Then preorder visits left child (node.left) and right child (node.right).