It said to not use any additional memory but I needed nonDup , count and next

class Solution {
  moveElements(arr) {
    // TODO: Write your code here
    let nonDup = 1;
    let count = 0;
    for (let next=0; next<arr.length; next++) {
      if (next === 0) continue;
      if (arr[next] !== arr[next-1]) {
        arr[nonDup] = arr[next]
        nonDup++;
        count++
      }
    }
    return count + 1;
  }
}