class Solution:
  def reverseVowels(self, s: str) -> str:
    # We need a way to do membership checks
    # and a set is a good way, since our reference
    # set isn't very large.
    vowels = set('aAeEiIoOuU')
    # Conver the string to a list so its easier to process
    s_list = [c for c in s]

    # Notice how the vowels switch sides?
    # hello -> holle, this tells me they're
    # processing the string from both ends
    # which means this is a good candidate for
    # two pointers
    l, r = 0, len(s) - 1

    # Non inclusive because you can't flip the middle
    # onto itself
    while l < r:
      # The problem doesn't seem to mention we'll be dealing
      # with spaces...so I don't think there's a need to check
      # This line checks whether each index in the string contains
      # a vowel
      if s_list[l] in vowels and s_list[r] in vowels:
        # If it does, we just switch them
        s_list[l], s_list[r] = s_list[r], s_list[l]
        # And shift our pointers
        l += 1
        r -= 1
      # If we don't encounter vowels, keep shifting pointers
      # Remember, we want to make sure we don't miss any vowels
      # in the case that one pointer is pointing to a vowel and
      # another is not
      elif s_list[l] not in vowels:
        l += 1
      elif s_list[r] not in vowels:
        r -= 1
    # Turn our result back into a string.
    return ''.join(s_list)