class Solution {
  moveElements(arr) {
    let read = 0;
    let lastUnique = 0;
    while (read < arr.length) {
      if (arr[read] !== arr[lastUnique]) { // found new unique value
        const write = Math.min(lastUnique + 1, read);
        arr[write] = arr[read];
        lastUnique = write;
      }
      read += 1;
    }
    return lastUnique + 1; // lengh = lastIndex + 1
  }
}