2.Add Two Numbers

      You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and  each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

      You may assume the two numbers do not contain any leading zero,except the number 0 itselsf.

 

 Approach 1:

 

public class ListNode{
      int val;
      ListNode next;
      ListNode(int x){
           val=x;
      }
}

public ListNode addTwoNumbers(ListNode l1,ListNode l2){
        ListNode listNode=new ListNode(0);
        ListNode node=listNode;
        int carry=0;
        while(l1!=null || l2!=null){
               int x=(l1!=null)?l1.val:0;
               int y=(l2!=null)?l2.val:0;
               int sum=x+y+carry;
               int carry=sum/10;
               node.next=new ListNode(sum%10);
               node=node.next;
               if(l1!=null){
                     l1=l1.next;
               }
               if(l2!=null){
                     l2=l2.next;
               }
        }
        if(carry>0){
               node.next=new ListNode(carry);
       }
       return listNode.next;
}