Javascript Program For Inserting Node In The Middle Of The Linked List (original) (raw)

Last Updated : 03 Sep, 2024

Given a linked list containing **n nodes. The problem is to insert a new node with data **x at the middle of the list. If **n is even, then insert the new node after the ****(n/2)**th node, else insert the new node after the ****(n+1)/2**th node.

**Examples:

**Input : list: 1->2->4->5
x = 3
**Output : 1->2->3->4->5

**Input : list: 5->10->4->32->16
x = 41
**Output : 5->10->4->41->32->16

**Method 1(Using length of the linked list):

Find the number of nodes or length of the linked using one traversal. Let it be **len. Calculate **c = (len/2), if **len is even, else **c = (len+1)/2, if **len is odd. Traverse again the first **c nodes and insert the new node after the **cth node.

JavaScript `

// Javascript implementation to insert node // at the middle of the linked list

let head; // head of list

/* Node Class */ class Node {

// Constructor to create a new node
constructor(d) {
    this.data = d;
    this.next = null;
}

}

// function to insert node at the // middle of the linked list function insertAtMid(x) { // if list is empty if (head == null) head = new Node(x); else { // get a new node let newNode = new Node(x);

    let ptr = head;
    let len = 0;

    // calculate length of the linked list
    // , i.e, the number of nodes
    while (ptr != null) {
        len++;
        ptr = ptr.next;
    }

    // 'count' the number of nodes after which
    // the new node is to be inserted
    let count = ((len % 2) == 0) ? (len / 2) :
        (len + 1) / 2;
    ptr = head;

    // 'ptr' points to the node after which
    // the new node is to be inserted
    while (count-- > 1)
        ptr = ptr.next;

    // insert the 'newNode' and adjust
    // the required links
    newNode.next = ptr.next;
    ptr.next = newNode;
}

}

// function to display the linked list function display() { let temp = head; while (temp != null) { console.log(temp.data); temp = temp.next; } }

// Driver program to test above

// Creating the list 1.2.4.5

head = new Node(1); head.next = new Node(2); head.next.next = new Node(4); head.next.next.next = new Node(5);

console.log("Linked list before insertion: "); display();

let x = 3; insertAtMid(x);

console.log("Linked list after insertion: "); display();

// This code contributed by Rajput-Ji

`

Output

Linked list before insertion: 1 2 4 5 Linked list after insertion: 1 2 3 4 5

Complexity Analysis:

**Method 2(Using two pointers):

Based on the tortoise and hare algorithm which uses two pointers, one known as **slow and the other known as **fast. This algorithm helps in finding the middle node of the linked list. It is explained in the front and black split procedure of this post. Now, you can insert the new node after the middle node obtained from the above process. This approach requires only a single traversal of the list.

JavaScript `

// Javascript implementation to insert node // at the middle of the linked list

let head; // head of list

/* Node Class */ class Node {

// Constructor to create a new node
constructor(val) {
    this.data = val;
    this.next = null;
}

}

// function to insert node at the // middle of the linked list function insertAtMid(x) { // if list is empty if (head == null) head = new Node(x);

else {
    // get a new node
    let newNode = new Node(x);

    // assign values to the slow
    // and fast pointers
    let slow = head;
    let fast = head.next;

    while (fast != null && fast.next != null) {
        // move slow pointer to next node
        slow = slow.next;

        // move fast pointer two nodes
        // at a time
        fast = fast.next.next;
    }

    // insert the 'newNode' and adjust
    // the required links
    newNode.next = slow.next;
    slow.next = newNode;
}

}

// function to display the linked list function display() { let temp = head; while (temp != null) { console.log(temp.data + " "); temp = temp.next; } }

// Driver program to test above

// Creating the list 1.2.4.5 head = null; head = new Node(1); head.next = new Node(2); head.next.next = new Node(4); head.next.next.next = new Node(5);

console.log("Linked list before insertion: "); display();

let x = 3; insertAtMid(x);

console.log("Linked list after insertion: "); display();

// This code is contributed by todaysgaurav

`

Output

Linked list before insertion: 1 2 4 5 Linked list after insertion: 1 2 3 4 5

Complexity Analysis:

Please refer complete article on Insert node into the middle of the linked list for more details!

Similar Reads

Mathematical

Recursion

Array

Searching

Sorting

Hashing

String

Linked List