2. Add Two Numbers leetcode java

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

两个非空链表代表分别代表一个整数，高位存在链表尾，低位存在链表头，相加后的结果存在链表里。

思路：

从链表头开始相加即可，设置进位符，结果一边计算一边存入新链表。

class Solution {    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {        if(l1==null)            return l2;        if(l2==null)            return l1;        int jw,add;        jw=0;        ListNode tail,p,q;//res为结果链表指针，tail为结果的链尾指针        ListNode res=new ListNode(-1);        tail=res;        p=l1;        q=l2;        while(p!=null&&q!=null){            add=p.val+q.val+jw;            jw=add/10;            add=add%10;            ListNode newnode=new ListNode(add);            tail.next=newnode;            tail=tail.next;            p=p.next;            q=q.next;        }        if(p==null){            while(q!=null){                add=q.val+jw;                jw=add/10;                add=add%10;                ListNode newnode=new ListNode(add);                tail.next=newnode;                tail=tail.next;                q=q.next;            }                    }        else if(q==null){            while(p!=null){                add=p.val+jw;                jw=add/10;                add=add%10;                ListNode newnode=new ListNode(add);                tail.next=newnode;                tail=tail.next;                p=p.next;            }                    }        if(jw!=0){            ListNode newnode=new ListNode(jw);            tail.next=newnode;        }                    return res.next;    }}

注意两个链表长度不一的情况，注意最后两个链表都遍历完但是有还有进位的情况。

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