public int[] removeDuplicate(int[] arr) {
        if (arr.length < 2) {
            return arr;
        }
        int l = 0;
        int r = 1;
        while (r < arr.length) {
            if (arr[l] != arr[r]) {
                arr[++l] = arr[r];
            }
            r++;
        }
        return Arrays.copyOf(arr, l + 1);
    }