两个链表相乘 字节三面算法题

题目

给你两个链表，返回第三个链表，第三个链表表示前两个链表的乘积，计算过程不能使用任何其他数据结构。
node节点结构

class Node {
        int v;
        Node next;

        Node(int v) {
            this.v = v;
        }
    }

示例
输入：
a:7->4->1
b:8->5->2
返回：
c:6->3->1->3->3->2

算法

public class Solution {
    static class Node {
        int v;
        Node next;

        Node(int v) {
            this.v = v;
        }
    }

    public static Node multiply(Node a, Node b) {
        Node node = multiplyIn(a, b);

        //对node节点进行进位处理
        int pre = 0;
        Node head = node;
        Node preNode = null;
        while (node != null) {
            int value = node.v;
            node.v = (value + pre) % 10;
            pre = (value + pre) / 10;
            preNode = node;
            node = node.next;
        }
        if (pre > 0) {
            preNode.next = new Node(pre);
        }
        return reverse(head);
    }

    public static Node multiplyIn(Node a, Node b) {
        //链表反转，便于计算
        Node aR = reverse(a);
        Node bR = reverse(b);

        Node tempA = aR;
        Node res = new Node(0);

        //对每一位相乘，把乘积只存在当前位中，比如十位和十位相乘，就把最后的结果存在百位中，最后再处理进位
        Node start = res;
        while (tempA != null) {

            Node tempB = bR;
            Node temp = start;
            while (tempB != null) {
                int value = tempA.v * tempB.v;
                temp.v += value;
                if (temp.next == null) {
                    temp.next = new Node(0);
                }
                tempB = tempB.next;
                temp = temp.next;
            }

            if (start.next == null) {
                start.next = new Node(0);
            }

            start = start.next;
            tempA = tempA.next;
        }
        return res;
    }

    private static Node reverse(Node node) {
        Node head = null;
        while (node != null) {
            Node next = node.next;
            node.next = head;
            head = node;
            node = next;
        }
        return head;
    }
}

测试

public static void main(String[] args) {
        Node a = new Node(7);
        a.next = new Node(4);
        a.next.next = new Node(1);
        a.next.next.next = new Node(8);
        a.next.next.next.next = new Node(5);
        a.next.next.next.next.next = new Node(2);

        Node b = new Node(8);
        b.next = new Node(5);
        b.next.next = new Node(2);
        b.next.next.next = new Node(9);
        b.next.next.next.next = new Node(6);
        b.next.next.next.next.next = new Node(3);

        Node result = multiply(a, b);
        while (result != null) {
            System.out.println(result.v + " ");
            result = result.next;
        }
    }