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GO Classes DPP | GATE DA | Python Programming | Insert Nodes

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3 3 votes

Consider the following Python code:

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

head = Node(20)
tail = head

new_first = Node(10)
new_first.next = head
head = new_first

new_last = Node(30)
tail.next = new_last
tail = new_last

print(head.data, head.next.data, tail.data, head.next.next.data)

What is the output of the code above?

  1. 10 20 30 30
  2. 20 10 30 30
  3. 10 30 30 20
  4. 10 20 20 30

1 Answer

1 1 vote

Initially:

head -> 20
tail -> 20

Now a new node is inserted at the beginning:

new_first = Node(10)
new_first.next = head
head = new_first

So the list becomes:

10 -> 20

The tail is still pointing to node $20$.

Now a new node is inserted at the end:

new_last = Node(30)
tail.next = new_last
tail = new_last

So the list becomes:

10 -> 20 -> 30

Therefore:

head.data = 10
head.next.data = 20
tail.data = 30
head.next.next.data = 30

The output is:

10 20 30 30

Correct Option: A

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