class Solution {

  public int moveElements(int[] arr) {
    int slow = 0, fast = 1, n = arr.length;

    while(fast < n && slow < n) {
      if(arr[slow] != arr[fast]) {
        slow++;
        arr[slow] = arr[fast];
      }
      fast++;
    }

    return slow + 1;
  }
}