LeetCode(2):Add Two Numbers

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

题意：将用链表表示的两个整数进行相加，其中整数的最低位在链表的头结点，最后的结果也是相同的表示形式。

思路：建立双指针，分别指向两个节结点，从个位逐位相加，并判断是否存在进位。最后再判断相加之后是否存在进位，如果存在则新建一个结点，结点元素值为1。

代码：

public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        if(l1==null) return l2;
        if(l2==null) return l1;
        int carry = 0;
        ListNode newHead = new ListNode(-1);
        
        ListNode l3= newHead;
        while(l1!=null || l2!=null){
            if(l1!=null){
                carry += l1.val;
                l1 = l1.next;
            }
            if(l2!=null){
                carry += l2.val;
                l2 = l2.next;
            }
            l3.next = new ListNode(carry%10);
            carry = carry / 10;
            l3=l3.next;
        }
        if(carry==1){
            l3.next = new ListNode(1);
        }
        return newHead.next;
        
    }