Remove Adjacent Repeated Characters II

Remove adjacent, repeated characters in a given string, leaving only two characters for each group of such characters. The characters in the string are sorted in ascending order.

Examples

“aaaabbbc” is transferred to “aabbc”

class Solution(object):
  def deDup(self, input):
    if not input or len(input) < 2:
      return input
    lst = list(input)
    left,right = 2,2
    while right < len(lst):
      if lst[right] != lst[left-2]:
        lst[left] = lst[right]
        left += 1
      right += 1
    return ''.join(lst[:left])