描述

报数序列是一个整数序列，按照其中的整数的顺序进行报数，得到下一个数。其前五项如下：

  1. 1

  2. 11

  3. 21

  4. 1211

  5. 111221

1 被读作 “one 1” (“一个一”) , 即 11。
11 被读作 “two 1s” (“两个一”）, 即 21。
21 被读作 “one 2”, “one 1” （“一个二” , “一个一”) , 即 1211。

给定一个正整数 n（1 ≤ n ≤ 30），输出报数序列的第 n 项。

注意：整数顺序将表示为一个字符串。

示例 1:

输入: 1
输出: “1”
示例 2:

输入: 4
输出: “1211”

Python

辣鸡题，可跳过
Idea here is keep track of the first letter in the sequence and count consecutive occurances. Once you encounter a new letter you add the previous count and letter to the chain. Repeat n-1 times (since we seeded the initial ‘1’ case). We always update temp after the inner loop since we will never have already added the last sequence.

 def countAndSay(self, n):
        s = '1'
        for _ in range(n-1):
            let, temp, count = s[0], '', 0
            for l in s:
                if let == l:
                    count += 1
                else:
                    temp += str(count)+let
                    let = l
                    count = 1
            temp += str(count)+let
            s = temp
        return s