Reversing a Linked List?!? 🤯

The following is attempt to understand to explain how to reverse a linked list in the simplest manner. First I will look at a linked list and then I’ll look at how to reverse it.

A linked list is NOT an array. Many people think it is but it is not.

A linked list “is a linear collection of data elements whose order is not given by their physical placement in memory. Instead, each element points to the next. It is a data structure consisting of a collection of nodes which together represent a sequence.” Wikipedia

In JavaScript a singly linked list can look like this (taken from an code example by Sarah Chima Atuonwu):

const list = {
    head: {
        value: 6
        next: {
            value: 10                                             
            next: {
                value: 12
                next: {
                    value: 3
                    next: null	
                    }
                }
            }
        }
    }
};

So a linked list is a unidirectional, one dimensional collection of nodes. It can algorithmically be represented this way as well:

head: {value: 6}, next: {value: 10}, next: {value: 12}, 
next: {value: 3}, next: null

Algorithmically it can also be represented like this:

(6) -> (10) -> (12) -> (3) -> null 

Creating a linked list is shown effectively in Sarah Chima Atuonwu’s blog: