leetcode: Add Two Numbers

很简单的一道链表题，注意边界条件，顺着做即可

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        int count = 0;
        if(l1 == null )
        {
            return l2;
        }
        if( l2 == null )
        {
            return l1;
        }
        ListNode res = new ListNode(0);
        ListNode pos = res;
        while( l1 != null || l2 != null )
        {
            int v1=0,v2=0;
            if( l1 != null )
            {
                v1 = l1.val;
                l1 = l1.next;
            }
            if( l2 != null )
            {
                v2 = l2.val;
                l2 = l2.next;
            }
            int tmp = v1+v2+count;
            if( tmp >= 10 )
            {
                count = 1;
                pos.val = tmp-10;
            }
            else
            {
                count = 0;
                pos.val = tmp;
            }
            
           
            if( l1 != null || l2 != null )
            {
                pos.next = new ListNode(0);
                pos = pos.next;
            }
            else if( count != 0 )
            {
                pos.next = new ListNode(1);
            }
        }
        return res;
        
        
        
    }
}