369. Plus One Linked List

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LeetCode

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Problem

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

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

Example 1:

Input: head = [1,2,3]
Output: [1,2,4]

Example 2:

Input: head = [0]
Output: [1]

Code

class Solution {
    public ListNode plusOne(ListNode head) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode notNine = dummy;

        while (head != null) {
            if (head.val != 9) {
                notNine = head;
            }
            head = head.next;
        }

        notNine.val++;
        notNine = notNine.next;

        while (notNine != null) {
            notNine.val = 0;
            notNine = notNine.next;
        }

    return dummy.val != 0 ? dummy : dummy.next;
  }
}