javascript - 将两个数字相加(Add Two Numbers Algo Understanding)

Question

I was doing following leetcode question:(我在做以下leetcode问题：)

You are given two non-empty linked lists representing two non-negative integers.(您将获得两个非空链表，它们代表两个非负整数。)

The digits are stored in reverse order and each of their nodes contain a single digit.(这些数字以相反的顺序存储，并且它们的每个节点都包含一个数字。) Add the two numbers and return it as a linked list.(将两个数字相加，并将其作为链表返回。)

You may assume the two numbers do not contain any leading zero, except the number 0 itself.(您可能会假设两个数字除了数字0本身以外都不包含任何前导零。)

For which I stumbled upon following algo(为此我偶然发现了算法)

function ListNode(val) {
      this.val = val;
      this.next = null;
 }

 //This functiomn is called
var addTwoNumbers = function(l1, l2) {    
    let remainder = 0
    let l3 = {}
    let head = l3
    while (l1 || l2 || remainder) {
        let sum = remainder
        function sumList (linkedList) {
            if (linkedList) {
                sum += linkedList.val
                return linkedList.next
            }
            return null
        }
        l1 = sumList(l1)
        l2 = sumList(l2)
        if (sum>9) {
            remainder = 1
            sum -= 10
        } else {
            remainder = 0
        }

        head.next = new ListNode(sum)
        head = head.next
    }
    return l3.next
};

Here, I am unable to comprehend the point of l3?(在这里，我无法理解l3的观点？)

If i remove it the algo fails?(如果我将其删除，算法会失败吗？)

Question Link: https://leetcode.com/problems/add-two-numbers/(问题链接： https : //leetcode.com/problems/add-two-numbers/)

  ask by anny123 translate from so

Answer 1

l3 is there to keep a record of all the values that have been changed for head.(l3在那里保留所有已更改为head的值的记录。)

If I say that:(如果我这样说：)

var a = {};
var b = a;

Then b is not its own object.(那么b不是它自己的对象。)

It's a pointer to the same exact object as a, so if you change a value in b, a updates to reflect that change as well.(它是与a相同的对象的指针，因此，如果您更改b中的值，则也会进行更新以反映该更改。)

That is still the case when you dive deeper into nested objects.(当您深入嵌套对象时，情况仍然如此。)

If I say that:(如果我这样说：)

var c = {value: 1, next:{innerValue: 1}};
var d = c;
d.value = 2;

Then c updates to reflect the new value as well, as I've already explained.(正如我已经解释的，然后c也会更新以反映新值。)

But the interesting part is that if I then go on to assign d to the nested object and edit the nested object, like so:(但是有趣的是，如果我继续将d分配给嵌套对象并编辑嵌套对象，如下所示：)

d = d.next;
d.innerValue = 2;

That still updates c!(仍然更新c！)

So c is keeping a record of all of these updates, while d is free to dive deeper into its nested objects.(因此，c保留所有这些更新的记录，而d可以自由地更深入地研究其嵌套对象。) After running this code, c and d will look like this:(运行此代码后，c和d将如下所示：)

console.log(c);//{value: 2, next:{innerValue: 2}}
console.log(d);//{innerValue: 2}

This is what l3 does.(这就是l3所做的。)

l3 is to head as c is to d, so when the algorithm says:(l3朝向c朝向d，所以当算法说：)

head.next = new ListNode(sum)
head = head.next

...you don't have to worry about losing your history because l3 is keeping a record of everything.(...您不必担心会丢失历史记录，因为l3会保留所有记录。)