[leetcode] 2. Add Two Numbers

题目：

You are given two non-empty linked lists representing two non-negative integers. 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.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

题解：

这道并不是什么难题，算法很简单，链表的数据类型也不难。就是建立一个新链表，然后把输入的两个链表从头往后撸，每两个相加，添加一个新节点到新链表后面，就是要处理下进位问题。还有就是最高位的进位问题要最后特殊处理一下。

public ListNode addTwoNumbers(ListNode l1,ListNode l2){ListNode root=new ListNode(-1);ListNode cur=root;int mark=0;ListNode node=null;while(l1!=null&&l2!=null){if(l1.val+l2.val+mark>10){node=new ListNode(l1.val+l2.val+mark-10);mark=1;}else{node=new ListNode(l1.val+l2.val+mark);mark=0;}cur.next=node;cur=cur.next;l1=l1.next;l2=l2.next;}while(l2!=null){if(l2.val+mark>10){node=new ListNode(l2.val+mark-10);mark=1;}else{node=new ListNode(l2.val+mark);mark=0;}cur.next=node;cur=cur.next;l2=l2.next;}while(l1!=null){if(l1.val+mark>10){node=new ListNode(l1.val+mark-10);mark=1;}else{node=new ListNode(l1.val+mark);mark=0;}cur.next=node;cur=cur.next;l1=l1.next;}if(mark==1)cur.next=new ListNode(1);return root.next;}