leetcode-38 Count and Say

38. Count and Say

Description

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

1
2
3
4
5
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.

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:

1
2
Input: 1
Output: "1"

Example 2:

1
2
Input: 4
Output: "1211"

Analyse

  1. 初始值为1，读作1个1，也就是11
  2. 值变为11, 读作2个1，也就是21
  3. 值变为21，读作1个2，1个1，也就是1211
  4. 值变为1211，读作1个1，1个2，2个1，也就是111221

输入一个n，给出经过n次此操作后的值