Add Two Numbers

You are given two linked lists representing two non-negative numbers. 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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
这题比较简单，就是一个大数据的加法。JAVA中有专门的一个类实现。BigInteger BigDecimal的源代码可以参考。
/**
* 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) {
              ListNode ln = new ListNode(0);
        int num = 0;
        ListNode end = ln;
       
        if(l1 == null&&l2!= null){
        ln = l2;
        }else if(l2 == null && l1 != null){
        ln = l1;
        }else if(l1 != null && l2 != null){

        ln.val = (l1.val+l2.val+num)%10;
        num = (l1.val+l2.val+num)/10;
        while(l1.next != null && l2.next != null){
        l1 = l1.next;
        l2 = l2.next;
        ln.next = new ListNode(0);
        ln = ln.next;
        ln.val = (l1.val+l2.val+num)%10;
        num = (l1.val+l2.val+num)/10;
        }
        if(l1.next == null && l2.next != null){
        while (l2.next!= null){
        ln.next = l2.next;
        l2 = l2.next;
        ln = ln.next;
        int val = l2.val;
        ln.val = (val+num)%10;
        num = (val+num)/10;
        }
       
        }else
        if(l2.next == null && l1.next != null){
        while (l1.next!= null){
        ln.next = l1.next;
        l1 = l1.next;
        ln = ln.next;
        int val = l1.val;
        ln.val = (val+num)%10;
        num = (val+num)/10;
        }
       
        }
        if(l1.next == null && l2.next == null){
        if(num == 1){
        ln.next = new ListNode(1);
        }
       
        }
        }
       
       
        return end;
    }
}
指针的运用。