Javascript Program For Insertion Sort In A Singly Linked List

Last Updated : 05 Sep, 2024

We have discussed Insertion Sort for arrays. In this article we are going to discuss Insertion Sort for linked list.

Below is a simple insertion sort algorithm for a linked list.

1) Create an empty sorted (or result) list.
2) Traverse the given list, do following for every node.
......a) Insert current node in sorted way in sorted or result list.
3) Change head of given linked list to head of sorted (or result) list.

The main step is (2.a) which has been covered in the post Sorted Insert for Singly Linked List

Below is the implementation of the above algorithm:

// Javascript program to sort link list
// using insertion sort
let head = null;
let sorted = null;

class node {
    constructor(val) {
        this.val = val;
        this.next = null;
    }
}

function push(val) {
    // Allocate node 
    let newnode = new node(val);

    // Link the old list off the 
    // new node 
    newnode.next = head;

    // Move the head to point to 
    // the new node 
    head = newnode;
}

// Function to sort a singly linked list 
// using insertion sort
function insertionSort(headref) {
    // Initialize sorted linked list
    let sorted = null;
    let current = headref;

    // Traverse the given linked list 
    // and insert every node to sorted
    while (current != null) {
        // Store next for next iteration
        let next = current.next;

        // Insert current in sorted 
        // linked list
        sortedInsert(current);

        // Update current
        current = next;
    }
    // Update head_ref to point to 
    // sorted linked list
    head = sorted;
}

/* Function to insert a new_node in a Linked List.
   Note that this function expects a pointer to 
   head_ref as this can modify the head of the 
   input linked list (similar to push()) */
function sortedInsert(newnode) {
    // Special case for the head end 
    if (sorted == null ||
        sorted.val >= newnode.val) {
        newnode.next = sorted;
        sorted = newnode;
    }
    else {
        let current = sorted;

        /* Locate the node before the point 
           of insertion */
        while (current.next != null &&
            current.next.val < newnode.val) {
            current = current.next;
        }
        newnode.next = current.next;
        current.next = newnode;
    }
}

// Function to print linked list 
function printlist(head) {
    while (head != null) {
        console.log(head.val);
        head = head.next;
    }
}

// Driver code 
push(5);
push(20);
push(4);
push(3);
push(30);
console.log("Linked List before Sorting..");
printlist(head);
insertionSort(head);
console.log("LinkedList After sorting");
printlist(sorted);
// This code is contributed by aashish1995

Output

Linked List before Sorting..
30
3
4
20
5
LinkedList After sorting
3
4
5
20
30

Complexity Analysis:

Time Complexity: O(n²), in the worst case, we might have to traverse all nodes of the sorted list for inserting a node, and there are “n” such nodes.
Space Complexity: O(1), no extra space is required depending on the size of the input, thus it is constant.

Please refer complete article on Insertion Sort for Singly Linked List for more details!