2. add two numbers

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        int carry = 0;
        int index_sum = 0;
        ListNode p = null;
        ListNode tmp = null;
        ListNode tmp1 = l1;
        ListNode tmp2 = l2;
        int val1,val2;
        while(tmp1 != null || tmp2 != null) {
            val1 = tmp1 != null ? tmp1.val : 0;
            val2 = tmp2 != null ? tmp2.val : 0;
            index_sum = val1 + val2 + carry;
            if(index_sum > 9){
                index_sum = index_sum - 10;
                carry = 1;
            } 
            else {
                carry = 0; 
            }
            if(p == null) {
                tmp = new ListNode(index_sum);
                p = tmp;
            }
            else {
             tmp.next = new ListNode(index_sum);   
             tmp = tmp.next;
            }
            if(tmp1 != null) {
                tmp1 = tmp1.next;
            }
            if(tmp2 != null) {
                tmp2 = tmp2.next; 
            } 
        }
        if(carry == 1) {
            tmp.next = new ListNode(1);  
        }
        return p;
    }
}