問題描述

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.

AC程式碼

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode tmp = new ListNode(0);
        ListNode head = tmp;
 

        int carry = 0;
        int val = 0;
        while(l1 != null || l2 != null){ //即使 l1 和 l2 長度不一致也適用，極大地減少了程式碼量
            if(l1 == null) l1 = new ListNode(0); // 如果 l1 已經遍歷完了，l1 的下一個節點用 0 代替
            if(l2 == null) l2 = new ListNode(0); //同理
            val = l1.val + l2.val + carry; // 別忘了加進位
            carry =
 
 val / 10;
            tmp.next = new ListNode(val % 10);
            tmp = tmp.next;
            l1 = l1.next;
            l2 = l2.next;
        }
        if(carry != 0) tmp.next = new ListNode(carry); //別忘記了：最後如果有進位的話，要把進位加上
        return head.next;
    }
    
}