LeetCode - 2. Add to Numbers(Linked List, Recursion, Math)*

문제

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 contains a single digit. Add the two numbers and return the sum as a linked list.
You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example 1:

Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [7,0,8]
Explanation: 342 + 465 = 807.

Example 2:

Input: l1 = [0], l2 = [0]
Output: [0]

Example 3:

Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
Output: [8,9,9,9,0,0,0,1]

풀이

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        if(l1==null) return l2;
        if(l2==null) return l1;
        
        ListNode result = new ListNode(0);
        ListNode head = result;
        int carry=0; //합이 10보다 클 경우 보정용 변수
        
        while(l1!=null||l2!=null||carry!=0){
            int sum = carry+(l1==null?0:l1.val)+(l2==null?0:l2.val);
            head.next=new ListNode(sum%10);
            head=head.next;
            carry=sum/10;
            l1 = l1==null?null:l1.next;
            l2 = l2==null?null:l2.next;
        }
        
        return result.next;
    }
}