public static ListNode Merge_Recursion(ListNode l1, ListNode l2)
{
if (l1 == null)
{
return(l2);
}
else if (l2 == null)
{
return(l1);
}
if (l1.val <= l2.val)
{
l1.next = Merge_Recursion(l1.next, l2);
return(l1);
}
else
{
l2.next = Merge_Recursion(l1, l2.next);
return(l2);
}
}
//without discarding first element
//preparing node for the next iteration, that's why we need to check if next iteration is required
public static ListNode AddTwoNumbers2(ListNode l1, ListNode l2)
{
if (l1 == null && l2 == null)
{
return(null);
}
ListNode curr = new ListNode();
ListNode head = curr;
int carry = 0;
while (l1 != null || l2 != null || carry > 0)
{
int sum = carry;
if (l1 != null)
{
sum = sum + l1.val;
l1 = l1.next;
}
if (l2 != null)
{
sum = sum + l2.val;
l2 = l2.next;
}
carry = sum / 10;
curr.val = sum % 10;
if (l1 != null || l2 != null || carry > 0) //atleast one more iteration remaining
{
curr.next = new ListNode();
curr = curr.next;
}
}
return(head);
}
public ListNode(int val = 0, ListNode next = null)
{
this.val = val;
this.next = next;
}