How to Add Two Numbers Represented by Linked Lists

class LinkedList {
 
     Node head1, head2;
 
    static class Node {
 
        int data;
        Node next;
 
        Node(int d) {
            data = d;
            next = null;
        }
    }
 
    /* Adds contents of two linked lists and prints it */
    void addTwoLists(Node first, Node second) {
        Node start1 = new Node(0);
        start1.next = first;
        Node start2 = new Node(0);
        start2.next = second;
 
        addPrecedingZeros(start1, start2);
        Node result = new Node(0);
        if (sumTwoNodes(start1.next, start2.next, result) == 1) {
            Node node = new Node(1);
            node.next = result.next;
            result.next = node;
        }
        Node res=reverse_it(result.next);
        printList(res);
        
    }
    static Node reverse_it(Node head)
    {
        Node prev=null;
        Node curr=head,next=null;
        while(curr!=null)
        {
            next=curr.next;
            curr.next=prev;
            prev=curr;
            curr=next;
        }
        return prev;
    }
 
    /* Adds lists and returns the carry */
    private int sumTwoNodes(Node first, Node second, Node result) {
        if (first == null) {
            return 0;
        }
        int number = first.data + second.data + sumTwoNodes(first.next, second.next, result);
        Node node = new Node(number % 10);
        node.next = result.next;
        result.next = node;
        return number / 10;
    }
 
    /* Appends preceding zeros in case a list is having lesser nodes than the other one*/
    private void addPrecedingZeros(Node start1, Node start2) {
        Node next1 = start1.next;
        Node next2 = start2.next;
        while (next1 != null && next2 != null) {
            next1 = next1.next;
            next2 = next2.next;
        }
        if (next1 == null && next2 != null) {
            while (next2 != null) {
                Node node = new Node(0);
                node.next = start1.next;
                start1.next = node;
                next2 = next2.next;
            }
        } else if (next2 == null && next1 != null) {
            while (next1 != null) {
                Node node = new Node(0);
                node.next = start2.next;
                start2.next = node;
                next1 = next1.next;
            }
        }
    }
 
    /* Utility function to print a linked list */
    void printList(Node head) {
        while (head != null) {
            System.out.print(head.data + " ");
            head = head.next;
        }
        System.out.println("");
    }
 
    // Driver Code
    public static void main(String[] args) {
        LinkedList list = new LinkedList();
 
        // creating first list
        list.head1 = new Node(1);
        list.head1.next = new Node(5);
        
 
        // creating second list
        list.head2 = new Node(3);
        list.head2.next = new Node(9);
        list.head2.next.next = new Node(7);
        
        System.out.print("Resultant List is ");
        // add the two lists and see the result
        list.addTwoLists(list.head1, list.head2);
    }
}

class Node:

	def __init__(self, data):
		self.data = data
		self.next = None

class LinkedList:

	def __init__(self):
		self.head = None

	def push(self, new_data):
		new_node = Node(new_data)
		new_node.next = self.head
		self.head = new_node

	def addTwoLists(self, first, second):
		prev = None
		temp = None
		carry = 0

		while(first is not None or second is not None):

			fdata = 0 if first is None else first.data
			sdata = 0 if second is None else second.data
			Sum = carry + fdata + sdata

			carry = 1 if Sum >= 10 else 0

			Sum = Sum if Sum < 10 else Sum % 10

			temp = Node(Sum)

			if self.head is None:
				self.head = temp
			else:
				prev.next = temp

			prev = temp

			if first is not None:
				first = first.next
			if second is not None:
				second = second.next

		if carry > 0:
			temp.next = Node(carry)

	def printList(self):
		temp = self.head
		while(temp):
			print (temp.data,end=' ')
			temp = temp.next


first = LinkedList()
second = LinkedList()

first.push(1)
first.push(5)

second.push(3)
second.push(9)
second.push(7)

res = LinkedList()
res.addTwoLists(first.head, second.head)

res.printList()

class Node 
{
    int val;
    Node next;
    Node(int value)
    {
        val = value;
        next = null;
    }
}
class AddTwoLL 
{
    static void push_front(Node head, int new_val)
    {
        Node new_node = new Node(new_val);
        new_node.next =head;
        head = new_node;
    }
    static void printList(Node head)
    {
        Node i = head;
        while(i!=null)
        {
            System.out.print(i.val+" ");
            i = i.next;
        }
        System.out.println();
    }
    // function to reverse a linked list
    static Node reverse_it(Node head)
    {
        Node prev = null;
        Node curr = head, next;
        while(curr!=null)
        {
            next = curr.next;
            curr.next = prev;
            prev = curr;
            curr = next;
        }
        return prev;
    }
    // function to convert a linked list to integer
    static int to_integer(Node head){
        int num = 0;
        Node curr = head;
        while(curr!=null)
        {
            int digit = curr.val;
            num = num*10 + digit;
            curr = curr.next;
        }
        return num;
    }
    // function to convert a number to a linked list containing digits in reverse order
    static Node to_linkedlist(int x)
    {
        Node head = new Node(0);
        if(x==0) return head;
        Node curr = head;
        while(x>0)
        {
            int d = x%10;
            x /= 10;
            curr.next = new Node(d);
            curr = curr.next;
        }
        return head.next;
    }
    // function to add 2 numbers given as linked lists
    static Node add_list(Node l1, Node l2)
    {
        // reversing the 2 linked lists
        l1 = reverse_it(l1);
        l2 = reverse_it(l2);
    
        // converting them into integers
        int num1 = to_integer(l1);
        int num2 = to_integer(l2);
        
        int sum = num1 + num2;
        // converting the sum back to
        // a linked list
        Node ans = to_linkedlist(sum);
        
        return ans;
    }
    public static void main(String [] args)
    {
        Node l1 = null;
    
        push_front(l1, 1);
        push_front(l1, 5);
    
        Node l2 = null;
    
        push_front(l2, 3);
        push_front(l2, 9);
        push_front(l2, 7);
    
        // l1-> 5 1
        // l2-> 7 9 3
    
        Node sum = add_list(l1,l2);
    
        printList(sum);
        // 2 1 4
    }
}