add-two-numbers.java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        
        if(l1==null||l2==null)
        {
            if(l1==null)
                return l2;
            else 
                return l1;        
        }
        ListNode head=new ListNode(-1);
        ListNode itr=head;
        int carry=0;
        while(l1!=null||l2!=null||carry!=0)
        {
            int sum=carry+(l1!=null?l1.val:0)+(l2!=null?l2.val:0);
            int digit=sum%10;
            carry=sum/10;
            ListNode dummy=new ListNode(digit);
            itr.next=dummy;
            itr=itr.next;
            if(l1!=null)
                l1=l1.next;
            if(l2!=null)
                l2=l2.next;
        }
        return head.next;
    }
}