38. Count and Say leetcode python 2016 new season

The count-and-say sequence is the sequence of integers beginning as follows:

1, 11, 21, 1211, 111221, ...

1

 is read off as 

"one
1"

 or 

11

.

11

 is read off as 

"two
1s"

 or 

21

.

21

 is read off as 

"one
2

, then 

one 1"

 or 

1211

.

Given an integer n, generate the nth sequence.

Note: The sequence of integers will be represented as a string.

class Solution(object):
def countAndSay(self, n):
"""
:type n: int
:rtype: str
"""
if n == 1:
return '1'
else:
prev = self.countAndSay(n - 1)
start = 0
res = ''
while start < len(prev):
count = 0
cur = prev[start]
while start < len(prev) and cur == prev[start]:
start += 1
count += 1
res += str(count) + cur
return res