addOne.java

class GfG {
    private Node reverse(Node head) {
        Node curr = head;
        Node prev = null;
        Node next = null;
        while (curr != null) {
            next = curr.next;
            curr.next = prev;
            prev = curr;
            curr = next;
        }
        return prev;
    }
    public void addOne(Node head) {
        if (head == null)
            return;
        Node curr = head;
        int carry = 1;
        Node prev = null;
        while (curr != null) {
            int sum = curr.data + carry;
            if (sum > 9) {
                carry = 1;
            } else {
                carry = 0;
            }
            curr.data = sum % 10;
            prev = curr;
            curr = curr.next;
        }

        if (carry > 0) {
            prev.next = new Node(1);
            prev.next.next = null;
            //head = prev.next;
        }
        Node correct_head = reverse(head);
        while (correct_head != null) {
            System.out.print(correct_head.data);
            correct_head = correct_head.next;
        }
        System.out.println();
    }


}