The count-and-say sequence is the sequence of integers with the first five terms as following:
1.     1
2.     11
3.     21
4.     1211
5.     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.
读n次字符串，按照几个几读出来

写一个函数读一次，然后循环或递归即可