Boundary Traversal of Binary Tree in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a node is a leaf node.

DSA Javascript

function isLeaf(node) {
  return node.left === null && node.[1] === null;
}

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

Aright

Bleft

Cvalue

Dparent

Attempts:

3 left

💡 Hint

Common Mistakes

Checking only one child instead of both.

Using wrong property names like 'value' or 'parent'.

A node is a leaf if both its left and right children are null. Here, we check if node.right is null.

2fill in blank

medium

Complete the code to add the left boundary nodes (excluding leaves) to the result array.

DSA Javascript

function addLeftBoundary(node, result) {
  let curr = node.left;
  while (curr !== null) {
    if (!isLeaf(curr)) result.push(curr.value);
    curr = curr.[1];
  }
}

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

Aright

Bleft

Cparent

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Moving down right child instead of left.

Adding leaf nodes to the boundary.

To traverse the left boundary, move down the left child nodes using curr.left.

3fill in blank

hard

Fix the error in the function that adds leaf nodes to the result array.

DSA Javascript

function addLeaves(node, result) {
  if (node === null) return;
  if (isLeaf(node)) {
    result.push(node.[1]);
    return;
  }
  addLeaves(node.left, result);
  addLeaves(node.right, result);
}

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

Aparent

Bleft

Cvalue

Dright

Attempts:

3 left

💡 Hint

Common Mistakes

Pushing the left or right child instead of the node's value.

Using undefined properties like 'parent'.

Leaf nodes hold their data in the 'value' property, which should be added to the result.

4fill in blank

hard

Fill both blanks to add the right boundary nodes (excluding leaves) in reverse order.

DSA Javascript

function addRightBoundary(node, result) {
  let curr = node.[1];
  const stack = [];
  while (curr !== null) {
    if (!isLeaf(curr)) stack.push(curr.value);
    curr = curr.[2];
  }
  while (stack.length > 0) {
    result.push(stack.pop());
  }
}

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

Aright

Bleft

Cparent

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using left child to start the right boundary.

Not reversing the collected nodes before adding.

Start from the right child and move down right children to collect right boundary nodes in reverse.

5fill in blank

hard

Fill the blank to complete the boundary traversal function.

DSA Javascript

function boundaryTraversal(root) {
  if (root === null) return [];
  const result = [root.[1]];
  addLeftBoundary(root, result);
  addLeaves(root.left, result);
  addLeaves(root.right, result);
  addRightBoundary(root, result);
  return result;
}

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

Aslice

Bpush

Cpop

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Adding leaves from root instead of its subtrees.

Wrong order of adding boundaries and leaves.

Forgetting to handle null root.

Start with root's value, add left boundary and leaves from subtrees, then add right boundary to the result array.

Practice

1. What is the main purpose of Boundary Traversal in a binary tree?

easy

A. To print all leaf nodes only

B. To print all nodes on the boundary in an anti-clockwise direction

C. To print nodes level by level

D. To print nodes in in-order traversal

Solution

1. Step 1: Understand boundary traversal definition

   Boundary traversal prints nodes on the edges of the tree, including left boundary, leaves, and right boundary.

2. Step 2: Compare options with definition

   Only To print all nodes on the boundary in an anti-clockwise direction describes printing all boundary nodes in anti-clockwise order.

3. Final Answer:

   To print all nodes on the boundary in an anti-clockwise direction -> Option B

4. Quick Check:

   Boundary traversal = print boundary nodes anti-clockwise [OK]

Hint: Boundary traversal prints edges and leaves anti-clockwise [OK]

Common Mistakes:

• Confusing boundary traversal with leaf node traversal
• Thinking it prints nodes level-wise
• Mixing it with in-order traversal

2. Which of the following is the correct way to start the boundary traversal function in JavaScript?

easy

A. function boundaryTraversal(root) { console.log(root.right); }

B. function boundaryTraversal() { return root; }

C. function boundaryTraversal(root) { if (!root) return []; }

D. function boundaryTraversal(root) { return root.left; }

Solution

1. Step 1: Check function signature and base case

   The function should accept root and handle empty tree by returning empty array.

2. Step 2: Validate options

   function boundaryTraversal(root) { if (!root) return []; } correctly defines function with root parameter and returns empty array if root is null.

3. Final Answer:

   function boundaryTraversal(root) { if (!root) return []; } -> Option C

4. Quick Check:

   Function starts with root check and empty return [OK]

Hint: Always check for empty tree at start of traversal function [OK]

Common Mistakes:

• Omitting root parameter
• Not handling empty tree
• Returning wrong values at start

3. Given the binary tree:

      1
     / \
    2   3
   / \   \
  4   5   6
     / \  /
    7  8 9

What is the output of boundary traversal (anti-clockwise)?

medium

A. [1, 2, 4, 7, 8, 5, 9, 6, 3]

B. [1, 2, 4, 7, 8, 9, 6, 3, 5]

C. [1, 2, 4, 5, 7, 8, 9, 6, 3]

D. [1, 2, 4, 7, 8, 9, 6, 3]

Solution

1. Step 1: Identify left boundary nodes

   Left boundary (excluding leaves): 1, 2

2. Step 2: Identify leaf nodes left to right

   Leaves: 4, 7, 8, 9, 6

3. Step 3: Identify right boundary nodes bottom-up excluding leaves

   Right boundary: 3

4. Step 4: Combine in anti-clockwise order

   Boundary traversal: 1 (root), 2 (left boundary), 4 (leaf), 7, 8, 9, 6 (leaf), 3 (right boundary)

5. Final Answer:

   [1, 2, 4, 7, 8, 9, 6, 3] -> Option D

6. Quick Check:

   Boundary nodes combined anti-clockwise = [1, 2, 4, 7, 8, 9, 6, 3] [OK]

Hint: List left boundary, leaves, then right boundary reversed [OK]

Common Mistakes:

• Including internal nodes as leaves
• Adding right boundary leaves twice
• Wrong order of nodes

4. Consider this code snippet for boundary traversal in JavaScript:

function printLeaves(node, result) {
  if (!node) return;
  if (!node.left && !node.right) {
    result.push(node.data);
  }
  printLeaves(node.left, result);
  printLeaves(node.right, result);
}

What is the bug in this code?

medium

A. It visits leaves in left to right order correctly

B. It pushes non-leaf nodes into result

C. It visits leaves in wrong order (right before left)

D. It does not check for null node before recursion

Solution

1. Step 1: Analyze leaf detection and recursion order

   Code checks if node is leaf and pushes data, then recursively visits left then right child.

2. Step 2: Verify leaf order correctness

   Visiting left subtree before right ensures leaves are collected left to right.

3. Step 3: Check for bugs

   No bug found; code correctly collects leaves in left to right order.

4. Final Answer:

   It visits leaves in left to right order correctly -> Option A

5. Quick Check:

   Leaf nodes collected left to right = It visits leaves in left to right order correctly [OK]

Hint: Left subtree first ensures left-to-right leaf order [OK]

Common Mistakes:

• Thinking recursion order is reversed
• Assuming non-leaf nodes are pushed
• Missing base case check

5. You want to perform boundary traversal on a binary tree but exclude all leaf nodes that have even values. Which approach correctly adapts the traversal?

hard

A. Modify leaf collection to skip leaves with even values during traversal

B. Skip left and right boundary nodes if they are even

C. Only collect leaves and ignore boundaries

D. Collect all nodes and filter even leaves after traversal

Solution

1. Step 1: Understand boundary traversal parts

   Boundary traversal includes left boundary, leaves, and right boundary.

2. Step 2: Identify where to exclude even leaves

   Only leaf nodes need filtering; boundaries remain unchanged.

3. Step 3: Adapt leaf collection function

   Modify leaf collection to check leaf value and skip if even.

4. Final Answer:

   Modify leaf collection to skip leaves with even values during traversal -> Option A

5. Quick Check:

   Filter leaves during traversal, not boundaries [OK]

Hint: Filter leaves during leaf collection step only [OK]

Common Mistakes:

• Filtering boundary nodes incorrectly
• Filtering after traversal causing extra work
• Ignoring leaf filtering altogether