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Grokking the Coding Interview Patterns in Python

Swapping Nodes in a Linked List

Explore how to swap the values of the kth node from the beginning and the kth node from the end in a linked list. Understand in-place linked list manipulation techniques that optimize memory use and efficiency, helping you master this common coding interview problem.

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Statement

Given the head of a linked list and an integer, k, return the head of the linked list after swapping the values of the kthk^{th} node from the beginning and the kthk^{th} node from the end of the linked list.

Note: We’ll number the nodes of the linked list starting from 11 to nn.

Constraints:

  • The linked list will have n number of nodes.
  • 1≤1 \leq k ≤\leq n ≤500\leq 500
  • −5000≤-5000 \leq Node.value ≤5000\leq 5000

Examples

Understand the problem

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

Swapping Nodes in a Linked List

1.

What is the output if the following data is given as input?

linked list = 4 → 2 → 7 → 8 → 9 → 0 → 2

k = 3

A.

8 → 9 → 0 → 4 → 2 → 7 → 2

B.

7 → 2 → 4 → 0 → 9 → 8 → 2

C.

4 → 2 → 9 → 8 → 7 → 0 → 2

D.

2 → 9 → 0 → 4 → 2 → 7 → 8

1 / 4

Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
1
2
3
4
5
6

Try it yourself

Implement your solution in the following coding playground.

Python
usercode > Solution.py
# Definition for a Linked List node

# class ListNode:

#     def __init__(self, val=0, next=None):

#         self.val = val

#         self.next = next

from ds_v1.LinkedList.LinkedList import ListNode

            

def swap_nodes(head, k):



    # Replace this placeholder return statement with your code

    

    return head
Swapping Nodes in a Linked List