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Java Program to insert a new node at the middle of the singly linked list

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robaa
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2022-11-13
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In this program, we will create a singly linked list and add a new node at the middle of the list. To accomplish this task, we will calculate the size of the list and divide it by 2 to get the mid-point of the list where the new node needs to be inserted.

Consider the above diagram; node 1 represents the head of the original list. Let node New is the new node which needs to be added at the middle of the list. First, we calculate size which in this case is 4. So, to get the mid-point, we divide it by 2 and store it in a variable count. Node current will point to head. First, we iterate through the list till current points to the mid position. Define another node temp which point to node next to current. Insert the New node between current and temp

Algorithm

  • Create a class Node which has two attributes: data and next. Next is a pointer to the next node in the list.
  • Create another class InsertMid which has three attributes: head, tail, and size that keep tracks of a number of nodes present in the list.
  • addNode() will add a new node to the list:
    • Create a new node.
    • It first checks, whether the head is equal to null which means the list is empty.
    • If the list is empty, both head and tail will point to a newly added node.
    • If the list is not empty, the new node will be added to end of the list such that tail's next will point to a newly added node. This new node will become the new tail of the list.

a. addInMid() will add a new node at the middle of the list:

  • It first checks, whether the head is equal to null which means the list is empty.
  • If the list is empty, both head and tail will point to a newly added node.
  • If the list is not empty, then calculate the size of the list and divide it by 2 to get mid-point of the list.
  • Define node current that will iterate through the list until current will point to the mid node.
  • Define another node temp which will point to node next to current.
  • The new node will be inserted after current and before temp such that current will point to the new node and the new node will point to temp.

a. display() will display the nodes present in the list:

  • Define a node current which will initially point to the head of the list.
  • Traverse through the list till current points to null.
  • Display each node by making current to point to node next to it in each iteration.
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robaa
2022-11-13
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Program:

public class InsertMid {  
  
    //Represent a node of the singly linked list  
    class Node{  
        int data;  
        Node next;  
  
        public Node(int data) {  
            this.data = data;  
            this.next = null;  
        }  
    }  
  
    public int size;  
    //Represent the head and tail of the singly linked list  
    public Node head = null;  
    public Node tail = null;  
  
    //addNode() will add a new node to the list  
    public void addNode(int data) {  
        //Create a new node  
        Node newNode = new Node(data);  
  
        //Checks if the list is empty  
        if(head == null) {  
            //If list is empty, both head and tail will point to new node  
            head = newNode;  
            tail = newNode;  
        }  
        else {  
            //newNode will be added after tail such that tail's next will point to newNode  
            tail.next = newNode;  
            //newNode will become new tail of the list  
            tail = newNode;  
        }  
        //Size will count the number of nodes present in the list  
        size++;  
    }  
  
    //This function will add the new node at the middle of the list.  
    public void addInMid(int data){  
        //Create a new node  
        Node newNode = new Node(data);  
  
        //Checks if the list is empty  
        if(head == null) {  
            //If list is empty, both head and tail would point to new node  
            head = newNode;  
            tail = newNode;  
        }  
        else {  
            Node temp, current;  
            //Store the mid position of the list  
            int count = (size % 2 == 0) ? (size/2) : ((size+1)/2);  
            //Node temp will point to head  
            temp = head;  
            current = null;  
  
            //Traverse through the list till the middle of the list is reached  
            for(int i = 0; i < count; i++) {  
                //Node current will point to temp  
                current = temp;  
                //Node temp will point to node next to it.  
                temp = temp.next;  
            }  
  
            //current will point to new node  
            current.next = newNode;  
            //new node will point to temp  
            newNode.next = temp;  
        }  
        size++;  
    }  
  
    //display() will display all the nodes present in the list  
    public void display() {  
        //Node current will point to head  
        Node current = head;  
        if(head == null) {  
            System.out.println("List is empty");  
            return;  
        }  
  
        while(current != null) {  
            //Prints each node by incrementing pointer  
            System.out.print(current.data + " ");  
            current = current.next;  
        }  
        System.out.println();  
    }  
  
    public static void main(String[] args) {  
  
        InsertMid sList = new InsertMid();  
  
        //Adds data to the list  
        sList.addNode(1);  
        sList.addNode(2);  
  
        System.out.println("Original list: ");  
        sList.display();  
  
        //Inserting node '3' in the middle  
        sList.addInMid(3);  
        System.out.println( "Updated List: ");  
        sList.display();  
  
        //Inserting node '4' in the middle  
        sList.addInMid(4);  
        System.out.println("Updated List: ");  
        sList.display();  
    }  
}

Output:

Original list: 
1 2 
Updated List: 
1 3 2 
Updated List: 
1 3 4 2

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