Binary Tree Node Structure in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the constructor method for a binary tree node.

DSA Python

class Node:
    def __init__(self, value):
        self.value = value
        self.left = None
        self.[1] = None

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

Aright

Bparent

Cchild

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'parent' or 'next' instead of 'right' for the right child pointer.

The right child of a binary tree node is stored in self.right. This completes the node structure with left and right pointers.

2fill in blank

medium

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

DSA Python

root = Node([1])

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

A'10'

Bnode

C10

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Passing '10' as a string instead of 10 as an integer.

The value passed to the node constructor should be an integer 10, not a string or other type.

3fill in blank

hard

Fix the error in the code to assign a left child node to root.

DSA Python

root.left = Node([1])

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

A5

BNone

Croot

D'left'

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning root or None as the value instead of an integer.

The left child node should be created with a value like 5, not with root or None.

4fill in blank

hard

Fill both blanks to check if a node has no children (is a leaf).

DSA Python

def is_leaf(node):
    return node.left is [1] and node.[2] is None

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

ANone

BFalse

Cright

DTrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using True or False instead of None for child checks.

Using wrong attribute names like 'child' or 'next'.

A leaf node has both left and right children as None. So we check if node.left is None and node.right is None.

5fill in blank

hard

Fill all three blanks to create a node, assign left and right children with values 1 and 2.

DSA Python

root = Node([1])
root.left = Node([2])
root.[3] = Node(2)

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

A0

B1

Cright

Dleft

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up left and right child assignments.

Using wrong values for node creation.

The root node is created with value 0, left child with 1, and right child assigned using root.right.

Practice

1. What does a typical binary tree node contain in its structure?

easy

A. A value and a reference to the parent node only

B. Only a value and a reference to the next node

C. A value, a reference to the left child, and a reference to the right child

D. A value and a list of all children nodes

Solution

1. Step 1: Understand binary tree node components

   A binary tree node typically stores a value and has two child references: left and right.

2. Step 2: Compare options with definition

   A value, a reference to the left child, and a reference to the right child matches this structure exactly, while others describe different data structures.

3. Final Answer:

   A value, a reference to the left child, and a reference to the right child -> Option C

4. Quick Check:

   Binary tree node = value + left + right [OK]

Hint: Binary tree nodes always have left and right child pointers [OK]

Common Mistakes:

• Confusing binary tree node with linked list node
• Thinking nodes have parent pointers by default
• Assuming children are stored in a list

2. Which of the following is the correct Python syntax to define a binary tree node class with attributes val, left, and right?

easy

A. class Node:
def __init__(self, val):
val = self
left = None
right = None

B. class Node:
def __init__(self, val):
self.val = val
self.left = None
self.right = None

C. class Node:
def __init__(self):
self.val = None
self.left = None
self.right = None

D. class Node:
def __init__(self, val, left, right):
self.val = val
self.left = left
self.right = right

Solution

1. Step 1: Check constructor parameters and attribute assignments

   class Node: def __init__(self, val): self.val = val self.left = None self.right = None correctly initializes val and sets left and right to None by default.

2. Step 2: Validate syntax correctness

   class Node: def __init__(self, val): val = self left = None right = None incorrectly assigns variables; class Node: def __init__(self): self.val = None self.left = None self.right = None misses val parameter; class Node: def __init__(self, val, left, right): self.val = val self.left = left self.right = right requires left and right on init which is less common.

3. Final Answer:

   class Node: def __init__(self, val): self.val = val self.left = None self.right = None -> Option B

4. Quick Check:

   Constructor sets val and initializes children to None [OK]

Hint: Init val, set left and right to None inside __init__ [OK]

Common Mistakes:

• Not using self to assign attributes
• Forgetting to initialize left and right
• Incorrect parameter order or missing parameters

3. What will be the output of the following code snippet?

class Node:
    def __init__(self, val):
        self.val = val
        self.left = None
        self.right = None

root = Node(10)
root.left = Node(5)
root.right = Node(15)
print(root.left.val, root.right.val)

medium

A. 15 5

B. 10 5

C. None None

D. 5 15

Solution

1. Step 1: Trace node creation and assignments

   Root node has value 10; left child is assigned a node with value 5; right child assigned node with value 15.

2. Step 2: Print left and right child values

   Printing root.left.val and root.right.val outputs 5 and 15 respectively.

3. Final Answer:

   5 15 -> Option D

4. Quick Check:

   Left child val = 5, Right child val = 15 [OK]

Hint: Print left.val and right.val after assignment to get child values [OK]

Common Mistakes:

• Printing root.val instead of children
• Confusing left and right child values
• Assuming children are None without assignment

4. Identify the error in the following binary tree node class definition:

class Node:
    def __init__(self, val):
        val = self.val
        left = None
        right = None

medium

A. Attributes are assigned incorrectly; should use self.val, self.left, self.right

B. Missing return statement in __init__ method

C. Class name should be lowercase

D. No error; code is correct

Solution

1. Step 1: Review attribute assignments in __init__

   Attributes must be assigned to self to belong to the instance, e.g., self.val = val.

2. Step 2: Identify incorrect assignments

   Code assigns val = self.val which reverses assignment and does not use self for left and right.

3. Final Answer:

   Attributes must be assigned using self, not local variables -> Option A

4. Quick Check:

   Use self.attr = value to set instance variables [OK]

Hint: Always assign attributes with self.attribute = value [OK]

Common Mistakes:

• Assigning variables without self prefix
• Reversing assignment order
• Expecting return in __init__

5. Given the following binary tree node class, how would you create a tree with root value 1, left child 2, and right child 3, then print the root and its children values?

class Node:
    def __init__(self, val):
        self.val = val
        self.left = None
        self.right = None

hard

A. root = Node(1)
root.left = Node(2)
root.right = Node(3)
print(root.val, root.left.val, root.right.val)

B. root = Node(1, Node(2), Node(3))
print(root.val, root.left.val, root.right.val)

C. root = Node()
root.val = 1
root.left = 2
root.right = 3
print(root.val, root.left, root.right)

D. root = Node(1)
root.left = 2
root.right = 3
print(root.val, root.left, root.right)

Solution

1. Step 1: Create root node with value 1

   Use Node(1) to create root with val=1 and children None.

2. Step 2: Assign left and right children as Node instances

   Assign root.left = Node(2) and root.right = Node(3) to create child nodes properly.

3. Step 3: Print values of root and children

   Print root.val, root.left.val, root.right.val to get 1 2 3.

4. Final Answer:

   Use separate Node instances for children and print their val attributes -> Option A

5. Quick Check:

   Children must be Node objects, not integers [OK]

Hint: Assign children as Node objects, then print their val attributes [OK]

Common Mistakes:

• Assigning children as integers instead of Node objects
• Using constructor with extra parameters (not defined)
• Printing child nodes directly without .val