Merge Sort for Linked Lists in JavaScript

23 Jun, 2022
Prerequisite: Merge Sort for Linked Lists Merge sort is often preferred for sorting a linked list. The slow random-access performance of a linked list makes some other algorithms (such as quicksort) perform poorly, and others (such as heapsort) completely impossible.  In this post, Merge sort for linked list is implemented using JavaScript. Examples:
Input : 5 -> 4 -> 3 -> 2 -> 1 Output :1 -> 2 -> 3 -> 4 -> 5 Input : 10 -> 20 -> 3 -> 2 -> 1 Output : 1 -> 2 -> 3 -> 10 -> 20
javascript
<script> // Create Node of LinkedListfunction Node(data) {        this.node = data;        this.next = null;} // To initialize a linkedlistfunction LinkedList(list) {    this.head = list || null} // Function to insert The new Node into the linkedListLinkedList.prototype.insert = function(data) {         // Check if the linked list is empty        // so insert first node and lead head        // points to generic node        if (this.head === null)            this.head = new Node(data);         else {             // If linked list is not empty, insert the node            // at the end of the linked list            let list = this.head;            while (list.next) {                list = list.next;            }             // Now here list pointer points to last            // node let’s insert out new node in it            list.next = new Node(data)        }} // Function to print linkedListLinkedList.prototype.iterate = function() {         // First we will check whether out        // linked list is empty or node        if (this.head === null)            return null;         // If linked list is not empty we will        // iterate from each Node and prints        // it’s value store in “data” property         let list = this.head;         // we will iterate until our list variable        // contains the “Next” value of the last Node        // i.e-> null        while (list) {            document.write(list.node)            if (list.next)                document.write(' -> ')            list = list.next        }} // Function to mergesort a linked listLinkedList.prototype.mergeSort = function(list) {         if (list.next === null)            return list;         let count = 0;        let countList = list        let leftPart = list;        let leftPointer = list;        let rightPart = null;        let rightPointer = null;         // Counting the nodes in the received linkedlist        while (countList.next !== null) {            count++;            countList = countList.next;        }         // counting the mid of the linked list        let mid = Math.floor(count / 2)        let count2 = 0;         // separating the left and right part with        // respect to mid node in the linked list        while (count2 < mid) {            count2++;            leftPointer = leftPointer.next;        }         rightPart = new LinkedList(leftPointer.next);        leftPointer.next = null;         // Here are two linked list which        // contains the left most nodes and right        // most nodes of the mid node        return this._mergeSort(this.mergeSort(leftPart),                                this.mergeSort(rightPart.head))} // Merging both lists in a sorted mannerLinkedList.prototype._mergeSort = function(left, right) {         // Create a new empty linked list        let result = new LinkedList()         let resultPointer = result.head;        let pointerLeft = left;        let pointerRight = right;                          // If true then add left most node value in result,        // increment left pointer else do the same in        // right linked list.        // This loop will be executed until pointer's of        // a left node or right node reached null        while (pointerLeft && pointerRight) {            let tempNode = null;             // Check if the right node's value is greater than            // left node's value            if (pointerLeft.node > pointerRight.node) {                tempNode = pointerRight.node                pointerRight = pointerRight.next;            }            else {                tempNode = pointerLeft.node                pointerLeft = pointerLeft.next;            }             if (result.head == null) {                result.head = new Node(tempNode)                resultPointer = result.head            }            else {                resultPointer.next = new Node(tempNode)                resultPointer = resultPointer.next            }        }         // Add the remaining elements in the last of resultant        // linked list        resultPointer.next = pointerLeft;        while (resultPointer.next)            resultPointer = resultPointer.next             resultPointer.next = pointerRight         // Result is the new sorted linked list        return result.head;} // Initialize the objectlet l = new LinkedList();l.insert(10)l.insert(20)l.insert(3)l.insert(2)l.insert(1)// Print the linked listl.iterate() // Sort the linked listl.head = LinkedList.prototype.mergeSort(l.head) document.write('<br> After sorting : '); // Print the sorted linked listl.iterate()</script>
Output
10 -> 20 -> 3 -> 2 -> 1
After sorting : 1 -> 2 -> 3 -> 10 -> 20 
Time Complexity: O(n*log(n))Auxiliary Space: O(n)
simmytarika5
amankr0211
JavaScript-DS
Linked-List-Sorting
JavaScript
Linked List
Recursion
Sorting
Linked List
Recursion
Sorting
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