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) {
        ListNode dummy = new ListNode();
        ListNode curr = dummy;
        int carry = 0;
        while(l1 != null ||l2 != null ||carry != 0){
            int sum = carry;
            if(l1 != null){
                sum += l1.val;
                l1 = l1.next;
            }
            if(l2 != null){
                sum += l2.val;
                l2 = l2.next;
            }
            carry = sum/10; // between two integer divison,fractional part ignored
            curr.next = new ListNode(sum%10);
            curr = curr.next;
        }
        return dummy.next;
    }
}