2. Add Two Numbers

/**
 * 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) {
        ListNode temp = new ListNode();
        ListNode a1,a2,a3;
        a1=l1;
        a2=l2;
        a3=temp;
        int carry=0,num;
        while(a1!=null && a2!=null)
        {
            num=a1.val+a2.val+carry;
            carry=num/10;
            a1=a1.next;
            a2=a2.next;
            ListNode x = new ListNode();
            x.val = num%10;
            a3.next = x;
            a3 = a3.next;
        }
        while(a1!=null)
        {
            num = a1.val+carry;
            carry = num/10;
            a1=a1.next;
            ListNode x = new ListNode();
            x.val = num%10;
            a3.next = x;
            a3 = a3.next;
        }
        while(a2!=null)
        {
            num = a2.val+carry;
            carry = num/10;
            a2=a2.next;
            ListNode x = new ListNode();
            x.val = num%10;
            a3.next = x;
            a3 = a3.next;
        }
        if(carry != 0)
        {
            ListNode x = new ListNode();
            x.val = carry;
            a3.next = x;
            a3=a3.next;
        }
        a3.next = null;
       return temp.next;
    }
}