“Reverse Linked List” Javascript solution Cheat Sheet

The “Reverse Linked List” is in the easy category and is a good start for understanding more challenging algorithms using a linked list as a data structure. I will focus on explaining a solution that works and not on the O time and space complexity.

Challenge: “Given the head of a singly linked list, reverse the list, and return the reversed list.”LeetCode

Note:

// Singly linked list data structure
// Given head “Object”
// Reverse the list
// Return reversed list

Example:

input: head =[5,6,7,8,9,10]
  next
   | 
5 -> 6 -> 7 -> 8 -> 9 -> 10 -> null
|                         |
Head                     Tail
   
return: [10,9,8,7,6,5]
   next
    |
10 -> 9 -> 8 -> 7 -> 6 -> 5 -> null
 |                        |
Head                     Tail

Explanation:

Create variables to keep track of reassigned values and iterate until we reach the end of the linked list.

1.Create variables to keep track

let currentNode = head;
let previousNode = null;
let nextNode = null;

2.Iterate until the end of the linked list when the head is equal to null

while (currentNode){
}

3.Reassign nodes values

nextNode = currentNode.next;
currentNode.next = previousNode;
previousNode = currentNode;
currentNode = nextNode;

4.Return reversed list link

return previousNode;

Solution :

var reverseList = function(head) {
 
 let currentNode = head;
 let previousNode = null;
 let nextNode = null;
 
 while(currentNode ){
 
 nextNode = currentNode.next;
 currentNode.next = previousNode;
 previousNode = currentNode; 
 currentNode = nextNode; 
 }
 return previousNode;
};