LeetCode Top 100 Liked Questions 2.Add Two Numbers (Java版; Medium)

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LeetCode Top 100 Liked Questions 2.Add Two Numbers (Java版; Medium)

题目描述

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.

Example:

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

第一次做; 没有考虑到两个数位数不同的情况, 也没考虑到最后carry为1还要再创建一个节点的情况; 好处是创建了一个节点作为伪头结点; 初始化 → (执行→更新)^n

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        //input check
        if(l1==null||l2==null)
            return null;
        //
        ListNode head = new ListNode(0), curr = head;
        int carry=0, sum=0;
        while(l1!=null && l2!=null){
            sum = (l1.val + l2.val + carry) % 10;
            carry = (l1.val + l2.val + carry) / 10;
            curr.next = new ListNode(sum);
            //update
            l1 = l1.next;
            l2 = l2.next;
            curr = curr.next;
        }
        //两个数字位数可能不同,所以还得单独来两个while循环
        while(l1!=null){
            sum = (l1.val + carry) % 10;
            carry = (l1.val + carry) / 10;
            curr.next = new ListNode(sum);
            //update
            l1 = l1.next;
            curr = curr.next;
        }
        while(l2!=null){
            sum = (l2.val + carry) % 10;
            carry = (l2.val + carry) / 10;
            curr.next = new ListNode(sum);
            //update
            l2 = l2.next;
            curr = curr.next;
        }
        //细节!如果还有进位的话, 需要再创建一个节点
        if(carry==1)
            curr.next = new ListNode(1);

        return head.next;
    }
}