LeetCode刷题--Add Two Numbers

题目

原题地址

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.

Example

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

答题

此题思路上应该比较简单，但是需要考虑的情况会比较多：

• 逆向进位 243 + 564 = 708

• 两个lists的长度不同。

• 最后需要将进位树num补到列表中。

private int num = 0;

public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
    ListNode temp = null;
    ListNode returnNode = null;
    while (l1 != null || l2 != null) {
        int val2= (l2 == null) ? 0 : l2.val;
        int val1= (l1 == null) ? 0 : l1.val; 
        
        int x = (val1 + val2 + num) % 10;
        
        ListNode subNode = new ListNode(x);
        if (returnNode == null) {
            returnNode = subNode;
            temp = returnNode;
        } else {
            temp.next = subNode;
            temp = temp.next;
        }
        
        num = (val1 + val2 + num) / 10;
        
        l1 = l1 == null ? null : l1.next;
        l2 = l2 == null ? null : l2.next;
        
    }
    if(num != 0){
        temp.next=new ListNode(num);
    }
    return returnNode;
}