Binary Tree Node Structure in DSA Java - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the data field for the node value.

DSA Java

public class TreeNode {
    int [1];
    TreeNode left;
    TreeNode right;

    public TreeNode(int val) {
        this.val = val;
        left = null;
        right = null;
    }
}

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

Avalue

Bval

Cdata

DnodeVal

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'value' or 'data' instead of 'val' causes mismatch with constructor.

The node value is stored in the field named 'val' as per the constructor and usage.

2fill in blank

medium

Complete the code to assign the left child node.

DSA Java

public void setLeftChild(TreeNode [1]) {
    this.left = [1];
}

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

AleftNode

Bnode

Cchild

DleftChild

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different parameter name than declared causes errors.

The parameter name is 'child' and it is assigned to 'left'.

3fill in blank

hard

Fix the error in the constructor parameter name to match the field assignment.

DSA Java

public TreeNode(int [1]) {
    this.val = val;
    left = null;
    right = null;
}

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

Aval

Bvalue

Cdata

DnodeVal

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different parameter name causes 'val' to be undefined.

The parameter must be named 'val' to match the assignment 'this.val = val;'.

4fill in blank

hard

Fill both blanks to complete the method that returns true if the node is a leaf (no children).

DSA Java

public boolean isLeaf() {
    return this.left [1] null && this.right [2] null;
}

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

A==

B!=

C&&

D||

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' causes wrong leaf detection.

Using logical OR '||' instead of AND '&&' causes incorrect results.

A node is a leaf if both left and right are equal to null.

5fill in blank

hard

Fill all three blanks to complete the method that returns the number of children (0, 1, or 2).

DSA Java

public int childrenCount() {
    int count = 0;
    if (this.left [1] null) count++;
    if (this.right [2] null) count++;
    return [3];
}

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

A!=

B==

Ccount

Dthis.count

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '!=' in conditions causes wrong count.

Returning 'this.count' instead of local 'count' causes errors.

Count increments if left or right child is not null, then returns count.

Practice

1. What is the primary purpose of a TreeNode class in a binary tree?

easy

A. To perform tree traversal operations

B. To store only the root node of the tree

C. To store a value and references to left and right child nodes

D. To balance the binary tree automatically

Solution

1. Step 1: Understand the role of a node in a binary tree

   A node holds data and links to its children, enabling tree structure.

2. Step 2: Identify what the TreeNode class stores

   It stores a value and references (pointers) to left and right child nodes.

3. Final Answer:

   To store a value and references to left and right child nodes -> Option C

4. Quick Check:

   Node = value + left + right [OK]

Hint: Nodes hold data and links to children [OK]

Common Mistakes:

• Thinking TreeNode stores the whole tree
• Confusing node with traversal logic
• Assuming TreeNode balances the tree

2. Which of the following is the correct Java syntax to define a binary tree node class with integer data?

easy

A. class TreeNode { int data; TreeNode left; TreeNode right; }

B. class TreeNode { int data; TreeNode left; TreeNode right; TreeNode(int val) { data = val; } }

C. class TreeNode { int data; TreeNode left; TreeNode right; void TreeNode() {} }

D. class TreeNode { int data; TreeNode left, right; }

Solution

1. Step 1: Check class field declarations

   Fields for data, left, and right nodes must be declared properly.

2. Step 2: Verify constructor syntax

   Constructor should initialize data; class TreeNode { int data; TreeNode left; TreeNode right; TreeNode(int val) { data = val; } } correctly defines constructor.

3. Final Answer:

   class TreeNode { int data; TreeNode left; TreeNode right; TreeNode(int val) { data = val; } } -> Option B

4. Quick Check:

   Constructor initializes data correctly [OK]

Hint: Constructor must initialize data field [OK]

Common Mistakes:

• Missing constructor to set data
• Incorrect constructor syntax (void TreeNode())
• Declaring multiple variables incorrectly

3. Given the following code, what will be printed?

class TreeNode {
  int data;
  TreeNode left, right;
  TreeNode(int val) { data = val; }
}

public class Main {
  public static void main(String[] args) {
    TreeNode root = new TreeNode(10);
    root.left = new TreeNode(5);
    root.right = new TreeNode(15);
    System.out.println(root.left.data + "," + root.right.data);
  }
}

medium

A. 5,15

B. 10,5

C. 15,5

D. 10,15

Solution

1. Step 1: Create root node with data 10

   Root node data is 10, left and right are null initially.

2. Step 2: Assign left and right children with data 5 and 15

   root.left.data = 5, root.right.data = 15.

3. Step 3: Print left and right data

   Output is "5,15" from root.left.data and root.right.data.

4. Final Answer:

   5,15 -> Option A

5. Quick Check:

   Left=5, Right=15 [OK]

Hint: Print left and right node data directly [OK]

Common Mistakes:

• Printing root data instead of children
• Swapping left and right values
• Confusing node references

4. Identify the error in the following TreeNode class code:

class TreeNode {
  int data;
  TreeNode left, right;
  void TreeNode(int val) {
    data = val;
  }
}

medium

A. Constructor has void return type, so it's a method not a constructor

B. Missing semicolon after data declaration

C. left and right should be arrays, not single nodes

D. Class name and constructor name do not match

Solution

1. Step 1: Check constructor syntax

   Constructor should not have a return type; 'void' makes it a method.

2. Step 2: Confirm class and constructor names match

   Names match, so no error there.

3. Final Answer:

   Constructor has void return type, so it's a method not a constructor -> Option A

4. Quick Check:

   Constructor no return type [OK]

Hint: Constructor must not have a return type [OK]

Common Mistakes:

• Adding void before constructor name
• Confusing methods with constructors
• Thinking left/right must be arrays

5. You want to create a binary tree node class that also stores a parent node reference. Which of the following class definitions correctly adds this feature?

hard

A. class TreeNode { int data; TreeNode left, right, parent; TreeNode(int val) { data = val; } }

B. class TreeNode { int data; TreeNode left, right; TreeNode parent; TreeNode(int val) { data = val; parent = null; } }

C. class TreeNode { int data; TreeNode left, right; TreeNode parent; TreeNode(int val) { data = val; left = right = parent = null; } }

D. class TreeNode { int data; TreeNode left, right; TreeNode parent; TreeNode(int val, TreeNode p) { data = val; parent = p; } }

Solution

1. Step 1: Understand the need for parent reference initialization

   Parent reference should be set when node is created to link properly.

2. Step 2: Check constructor parameters and assignments

   class TreeNode { int data; TreeNode left, right; TreeNode parent; TreeNode(int val, TreeNode p) { data = val; parent = p; } } passes parent node as parameter and assigns it correctly.

3. Final Answer:

   class TreeNode { int data; TreeNode left, right; TreeNode parent; TreeNode(int val, TreeNode p) { data = val; parent = p; } } -> Option D

4. Quick Check:

   Parent passed and assigned in constructor [OK]

Hint: Pass parent node in constructor to set reference [OK]

Common Mistakes:

• Not initializing parent reference
• Setting parent to null always
• Declaring parent but never assigning