lc38. Count and Say1 is read off as "one 1" or 11. 11 is rea

Count and Say Easy

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

```
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 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

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']
>>>