class Solution:
  def sort(self, arr):
    b, m, e = 0, 0, len(arr) - 1
    while m <= e:
        if arr[e] == 2:
            e -= 1
        elif arr[b] == 0:
            # here is the tricky part if the middle pointer at same position as the position as the beginning pointer 
            # and the beginning pointer = 0 it meas we are done with that part of the array so we can safely 
            # move the middle pointer too together with the beginning pointer
            if m == b: 
                m += 1
            b += 1
        elif arr[m] == 1:
            m += 1
        elif arr[e] < arr[m]:
            # swap 
            arr[e], arr[m] = arr[m], arr[e]
        elif arr[m] < arr[b]:
            # swap
            arr[m], arr[b] = arr[b], arr[m]
    return arr