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

題意：給兩個鏈表，反向表示兩個數，如題幹所給兩個數分別是342和465，兩數相加結果爲807，轉換成鏈表爲7->0->8

思路：遍歷鏈表，逐位相加，有進位則加標記，在下一次相加是再加標記位。

實現：

/**
* 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 l=null,front=null,temp=null,i=l1,j=l2;
        l=new ListNode(0);
        front=l;
        int flag=0;
        while(i!=null||j!=null){
             int res=0;
             if(i==null)
                  res=j.val+flag;
             else if(j==null)
                  res=i.val+flag;
             else
                  res=i.val+j.val+flag;
             if(res<=9){
                  temp=new ListNode(res);
                  flag=0;
             }
             else{
                  temp=new ListNode(res-10);
                  flag=1;
             }
             front.next=temp;
             front=front.next;
             if(i==null)
                  j=j.next;
             else if(j==null)
                  i=i.next;
             else{
                  i=i.next;
                  j=j.next;
             }
            
        }
        if(flag==1){
             front.next=new ListNode(1);
        }
          return l.next;
    }
}