Create a Binary Tree Manually in DSA Java - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new node with value 10.

DSA Java

TreeNode root = new TreeNode([1]);

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

Anull

B10

Croot

D"10"

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around the number, which makes it a string.

Using null instead of a value.

The constructor needs an integer value. 10 is correct.

2fill in blank

medium

Complete the code to assign a left child node with value 5 to the root.

DSA Java

root.[1] = new TreeNode(5);

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

Aright

Bnode

Cchild

Dleft

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'right' instead of 'left'.

Using non-existent fields like 'child' or 'node'.

The left child of a binary tree node is assigned to the 'left' field.

3fill in blank

hard

Fix the error in the code to assign a right child node with value 15 to the root.

DSA Java

root.[1] = new TreeNode(15);

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

Aright

Bleftt

CRight

DchildRight

Attempts:

3 left

💡 Hint

Common Mistakes

Misspelling 'left' or 'right'.

Using uppercase letters in field names.

The correct field name for the right child is 'right' (all lowercase).

4fill in blank

hard

Fill both blanks to create a left child with value 3 and a right child with value 7 for the left node.

DSA Java

root.left.[1] = new TreeNode(3);
root.left.[2] = new TreeNode(7);

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

Aleft

Bright

Cchild

Dnode

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'child' or 'node' which are not valid fields.

Swapping left and right.

The left child is assigned to 'left' and the right child to 'right'.

5fill in blank

hard

Fill all three blanks to create a right child with value 20 for the right node, and a right child with value 25 for that right child.

DSA Java

root.right.[1] = new TreeNode(20);
root.right.[2].[3] = new TreeNode(25);

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

Aleft

Bright

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'left' instead of 'right' for these assignments.

Confusing the levels of the tree.

The right child of root.right is assigned to 'right'. Then its right child is assigned to 'right' again.

Practice

1. What is the correct way to create a root node of a binary tree manually in Java using a Node class with an integer value?

easy

A. Node root = new Node(); root.value = 10;

B. Node root = Node(10);

C. Node root = new Node.value(10);

D. Node root = new Node(10);

Solution

1. Step 1: Understand Node object creation

   In Java, to create an object, you use the new keyword followed by the constructor call.

2. Step 2: Apply correct syntax for constructor with value

   The constructor Node(10) creates a node with value 10. So new Node(10) is correct.

3. Final Answer:

   Node root = new Node(10); -> Option D

4. Quick Check:

   Object creation with constructor = new Node(10) [OK]

Hint: Use 'new' keyword with constructor to create objects [OK]

Common Mistakes:

• Omitting 'new' keyword
• Using incorrect constructor syntax
• Trying to assign value without constructor

2. Which of the following is the correct syntax to manually link a left child node with value 5 to a root node in Java?

easy

A. root.left = new Node(5);

B. root.leftNode = new Node(5);

C. root.left = Node(5);

D. root.left = new Node.left(5);

Solution

1. Step 1: Understand node linking in binary tree

   The left child of a node is usually accessed by left field. Assigning a new node requires new Node(value).

2. Step 2: Apply correct field and constructor syntax

   So root.left = new Node(5); correctly creates and links the left child.

3. Final Answer:

   root.left = new Node(5); -> Option A

4. Quick Check:

   Link left child with new Node = root.left = new Node(5) [OK]

Hint: Use 'root.left = new Node(value)' to link left child [OK]

Common Mistakes:

• Using wrong field name like leftNode
• Omitting 'new' keyword
• Incorrect constructor call without 'new'

3. Given the following code, what is the output of an inorder traversal (left, root, right)?

class Node {
  int value;
  Node left, right;
  Node(int v) { value = v; }
}

Node 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);

void inorder(Node node) {
  if (node == null) return;
  inorder(node.left);
  System.out.print(node.value + " ");
  inorder(node.right);
}

inorder(root);

medium

A. 4 2 5 1 3

B. 1 2 3 4 5

C. 1 3 2 4 5

D. 2 4 5 1 3

Solution

1. Step 1: Understand inorder traversal order

   Inorder visits left subtree, then root, then right subtree recursively.

2. Step 2: Trace traversal on given tree

   Left subtree of root(1) is node(2) with children 4 and 5.
   Traverse left subtree of 2: 4 (no children)
   Visit 2
   Traverse right subtree of 2: 5 (no children)
   Visit root 1
   Traverse right subtree of root: 3 (no children)
   Sequence: 4 2 5 1 3

3. Final Answer:

   4 2 5 1 3 -> Option A

4. Quick Check:

   Inorder = left, root, right = 4 2 5 1 3 [OK]

Hint: Inorder = left subtree, root, then right subtree [OK]

Common Mistakes:

• Confusing preorder or postorder with inorder
• Missing left or right subtree nodes
• Printing root before left subtree

4. Identify the error in the following code that tries to create a binary tree manually:

class Node {
  int value;
  Node left, right;
  Node(int v) { value = v; }
}

Node root = new Node(10);
root.left = Node(5);
root.right = new Node(15);

medium

A. Node class constructor is missing

B. Cannot assign right child after root creation

C. Missing 'new' keyword when creating left child node

D. Value type should be String, not int

Solution

1. Step 1: Check node creation syntax

   Creating a new node requires the 'new' keyword before constructor call.

2. Step 2: Identify incorrect line

   Line root.left = Node(5); misses 'new' keyword, causing syntax error.

3. Final Answer:

   Missing 'new' keyword when creating left child node -> Option C

4. Quick Check:

   Object creation needs 'new' keyword [OK]

Hint: Always use 'new' to create objects in Java [OK]

Common Mistakes:

• Omitting 'new' keyword
• Confusing constructor call with method call
• Assuming automatic object creation

5. You want to manually create a binary tree with root value 7, left child 3, right child 9, and left child's right child 5. Which code snippet correctly builds this tree?

hard

A. Node root = new Node(7);
root.left = new Node(3);
root.right = new Node(9);
root.right.left = new Node(5);

B. Node root = new Node(7);
root.left = new Node(3);
root.right = new Node(9);
root.left.right = new Node(5);

C. Node root = new Node(7);
root.left = new Node(3);
root.left.left = new Node(9);
root.left.right = new Node(5);

D. Node root = new Node(7);
root.right = new Node(3);
root.left = new Node(9);
root.left.right = new Node(5);

Solution

1. Step 1: Create root and direct children

   Root is 7, left child 3, right child 9, so assign accordingly.

2. Step 2: Add left child's right child

   Left child's right child is 5, so root.left.right = new Node(5); is correct.

3. Final Answer:

   Node root = new Node(7); root.left = new Node(3); root.right = new Node(9); root.left.right = new Node(5); -> Option B

4. Quick Check:

   Assign children correctly by following tree structure [OK]

Hint: Assign children stepwise matching tree structure [OK]

Common Mistakes:

• Swapping left and right children
• Assigning child to wrong parent node
• Missing intermediate child nodes