[Topic] add two numbers

Title Description

Here are two for you Non empty The linked list of , Represents two nonnegative integers . Each of them is based on The reverse Stored in , And each node can only store a Numbers .
Please add up the two numbers , And returns a linked list representing sum in the same form . You can assume that in addition to the numbers 0 outside , Neither of these numbers 0 start .

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

Solution

Scheme 1

 Insert a code chip here 

Option two

There is accuracy problem , Not recommended at present

public class Test {
    
    public static void main(String[] args) {
    

        int[] a = {
    1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1};
        int[] b = {
    5, 6, 4};

        System.out.println(addTwoNumbers(arrayToNode(a), arrayToNode(b)));
    }

    /** *  Array to linked list method  */
    public static ListNode arrayToNode(int[] arr) {
    
        ListNode head = new ListNode(arr[0]);
        ListNode other = head;
        for (int i = 1; i < arr.length; i++) {
    
            ListNode temp = new ListNode(arr[i]);
            other.next = temp;
            other = other.next;

        }// Printing nodes here can easily lead to head The change of 
        return head;
    }

    public static ListNode addTwoNumbers(ListNode l1, ListNode l2) {
    

        ArrayList<Long> nums1 = getNumsByLinkedList(l1);
        long n1 = getReversalNum(nums1);

        ArrayList<Long> nums2 = getNumsByLinkedList(l2);
        long n2 = getReversalNum(nums2);

        long sum = n1 + n2;

        String result = reverse(sum);

        // Head node 
        ListNode headNode = new ListNode(Character.getNumericValue(result.charAt(0)));
        // The cursor pointer points to the header node 
        ListNode cursor = headNode;
        for (int i = 1; i < result.length(); i++) {
    
            cursor.next = new ListNode(Character.getNumericValue(result.charAt(i)));
            cursor = cursor.next;
        }

        cursor = headNode;
        return cursor;
    }

    /** *  Number reversal  * * @param x  The value of the input  * @return  Flipped value  */
    public static String reverse(long x) {
    
        return new StringBuffer(String.valueOf(x)).reverse().toString();
    }

    /** *  According to the linked list , Get the array in the linked list  * * @param l  Linked list  * @return  The array inside  */
    private static ArrayList<Long> getNumsByLinkedList(ListNode l) {
    
        ArrayList<Long> nums = new ArrayList<>();

        while (true) {
    
            nums.add((long) l.val);
            if (l.next == null) {
    
                break;
            }
            l = l.next;
        }

        return nums;
    }

    /** *  Get the inverted number according to the array  *  for example [1, 2, 3] -> 321 * * @param nums  A collection of numbers  */
    private static long getReversalNum(ArrayList<Long> nums) {
    
        // Input verification 

        long result = 0;
        int length = nums.size();

        for (int i = length - 1; i >= 0; i--) {
    
            result += nums.get(i) * Math.pow(10, i);
        }

        return result;
    }
}

Title source ： Power button - Addition of two numbers