Plus One Linked List -- Leetcode

Question:

Given a non-negative number represented as a singly linked list of digits, plus one to the number.

The digits are stored such that the most significant digit is at the head of the list.

Example:

Input:
1->2->3

Output:
1->2->4

Answer:

public class Solution {

    public ListNode plusOne(ListNode head) {

        boolean flag = Util(head);

        if(flag){

            ListNode newHead = new ListNode(1);

            newHead.next = head;

            return newHead;

        }

        return head;

    }

    

    public boolean Util(ListNode node){

        if(node == null)return true;

        

        ListNode next = node.next;

        //DFS

        boolean flag = Util(next);

        

        if(flag){

           if(node.val == 9){

              node.val = 0;

              return true;

           }else{

              node.val += 1;

           }

        }

        return false;

    }

}