Questions regarding the algorithm question in LeetCode - Remove Duplicates from Sorted Array using Java

Question

I am working on an algorithm problem on Leetcode. But first I wrote my answer on my own local compiler. When running my code locally, I can get the answer to this question. But when I paste my answer directly into the online compiler on leetcode, the system prompts me that my answer is wrong. Cannot match the correct answer. The solution from my local compiler shown below:

class Solution {
    public int removeDuplicates(int[] nums) {
        ArrayList<Integer> list = new ArrayList<Integer>();
        ArrayList<Integer> arraylist = new ArrayList<Integer>();

        for (int i : nums) {
            list.add(i);
        }

        for (int num : list) {
            if (!arraylist.contains(num)) {
                arraylist.add(num);
            }
        }

        return arraylist.size();
    }
}

And the feedback from LeetCode: enter image description here

Answer 1

Some comments say that a set could be used, but the task is to do so without any additional memory allocation, the simplest solution is:

private static int removeDuplicates(int[] numbers) {
    int size = 0;
    for (int i = 0; i < numbers.length; i++) {
        if (i == 0 || numbers[i - 1] != numbers[i]) {
            numbers[size++] = numbers[i];
        }
    }
    return size;
}