class Solution:
def compress(self, chars: List[str]) -> int:
start = 0
end = 0
index = 0
while end < len(chars):
while end < len(chars) and chars[end] == chars[start]:
end += 1
chars[index] = chars[start]
index += 1
if end - start > 1:
for c in str(end - start):
chars[index] = c
index += 1
start = end
return index