LC.1180. Count Substrings with Only One Distinct Letter

class Solution:     def countLetters(self, S: str) -> int:         """         统计连续相同字符出现的次数即可         对于长度为n 的相同字符的字符串，他有 1+2+..n个子串         """         def sum_n(n):             return (n+1)*n //2         last_char, result, count, S = "$", 0, 0, S +"$"         for char in S:             if char == last_char:                 count += 1             else:                 result += sum_n(count)                 count = 1                 last_char = char         return result 

来源：51CTO

作者：很吵请安青争

链接：https://blog.csdn.net/dpengwang/article/details/100808049