Binary Tree Node Structure in DSA Typescript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Binary Tree Node Creation

What will be the printed output of the binary tree node after running the code below?

DSA Typescript

class TreeNode {
  val: number;
  left: TreeNode | null;
  right: TreeNode | null;
  constructor(val: number) {
    this.val = val;
    this.left = null;
    this.right = null;
  }
}

const root = new TreeNode(10);
root.left = new TreeNode(5);
root.right = new TreeNode(15);
console.log(root.val + ' -> ' + root.left?.val + ' -> ' + root.right?.val + ' -> null');

A 10 -> 5 -> 15 -> null

B 10 -> null -> null -> null

C 15 -> 5 -> 10 -> null

D 5 -> 10 -> 15 -> null

💡 Hint

Think about how the root node and its children are assigned values.

The root node has value 10, its left child is 5, and right child is 15. The print statement shows these values in order followed by null.

❓ Predict Output

intermediate

Value of Left Child After Node Modification

After running the code below, what is the value of root.left.val?

DSA Typescript

class TreeNode {
  val: number;
  left: TreeNode | null;
  right: TreeNode | null;
  constructor(val: number) {
    this.val = val;
    this.left = null;
    this.right = null;
  }
}

const root = new TreeNode(20);
root.left = new TreeNode(10);
root.left.val = 15;

A 15

B 10

C 20

D null

💡 Hint

Look at the line where root.left.val is changed.

The left child's value was initially 10 but then changed to 15 explicitly.

❓ Predict Output

advanced

Output of Inorder Traversal of Binary Tree

What is the output of the inorder traversal of the binary tree created by the code below?

DSA Typescript

class TreeNode {
  val: number;
  left: TreeNode | null;
  right: TreeNode | null;
  constructor(val: number) {
    this.val = val;
    this.left = null;
    this.right = null;
  }
}

function inorder(root: TreeNode | null, result: number[] = []): number[] {
  if (root === null) return result;
  inorder(root.left, result);
  result.push(root.val);
  inorder(root.right, result);
  return result;
}

const root = new TreeNode(8);
root.left = new TreeNode(3);
root.right = new TreeNode(10);
root.left.left = new TreeNode(1);
root.left.right = new TreeNode(6);
root.right.right = new TreeNode(14);
const output = inorder(root);
console.log(output.join(' -> ') + ' -> null');

A 8 -> 3 -> 1 -> 6 -> 10 -> 14 -> null

B 1 -> 3 -> 6 -> 8 -> 10 -> 14 -> null

C 1 -> 6 -> 3 -> 8 -> 14 -> 10 -> null

D 3 -> 1 -> 6 -> 8 -> 14 -> 10 -> null

💡 Hint

Inorder traversal visits left child, then node, then right child.

Inorder traversal visits nodes in ascending order for binary search trees. The sequence is left subtree (1,3,6), root (8), right subtree (10,14).

🔧 Debug

advanced

Identify the Error in Binary Tree Node Assignment

What error will the following code produce when run?

DSA Typescript

class TreeNode {
  val: number;
  left: TreeNode | null;
  right: TreeNode | null;
  constructor(val: number) {
    this.val = val;
    this.left = null;
    this.right = null;
  }
}

const root = new TreeNode(5);
root.left.val = 3;

A No error, runs successfully

B SyntaxError: Unexpected token '.'

C ReferenceError: root.left is not defined

D TypeError: Cannot read property 'val' of null

💡 Hint

Check if root.left is assigned before accessing its val property.

root.left is null by default. Trying to access val on null causes a TypeError.

🧠 Conceptual

expert

Number of Nodes in a Complete Binary Tree of Height h

What is the total number of nodes in a complete binary tree of height h (where height is the number of edges from root to deepest leaf)?

A h + 1

B 2^h - 1

C 2^(h+1) - 1

D h * 2

💡 Hint

Think about how nodes double at each level in a complete binary tree.

A complete binary tree of height h has nodes equal to sum of nodes at each level: 1 + 2 + 4 + ... + 2^h = 2^(h+1) - 1.