lc38. Count and Say

38. Count and Say Easy

791

6075

Favorite

Share The count-and-say sequence is the sequence of integers with the first five terms as following:

1. 1
   复制代码

2. 11
   复制代码

3. 21
   复制代码

4. 1211
   复制代码

5. 111221
   复制代码

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 where 1 ≤ n ≤ 30, generate the nth term of the count-and-say sequence.

Note: Each term of the sequence of integers will be represented as a string.

Example 1:

Input: 1 Output: "1" Example 2:

Input: 4 Output: "1211"

思路：groupby函数

代码：python3

class Solution:
    import itertools
    def countAndSay(self, n):
        s='1'
        for i in range(n-1):
            s=''.join(str(len(list(group)))+digit for digit,group in itertools.groupby(s))
        return s
复制代码

tips:

>>> for digit,group in itertools.groupby('11223344555666777'):
...     print(digit)
...     print(list(group))
... 
1
['1', '1']
2
['2', '2']
3
['3', '3']
4
['4', '4']
5
['5', '5', '5']
6
['6', '6', '6']
7
['7', '7', '7']
>>> 
复制代码

转载于:https://juejin.im/post/5d0af410e51d4576bc1a0e0f