38-Count and Say

题目描述：

https://leetcode.com/problems/count-and-say/

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.

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"

1.     1
 2.     11
 3.     21
 4.     1211
 5.     111221 
 6.     312211
 7.     13112221
 8.     1113213211
 9.     31131211131221
10.     13211311123113112211

解答：

package com.jack.algorithm;

/**
 * create by jack 2019/6/30
 *
 * @author jack
 * @date: 2019/6/30 16:19
 * @Description:
 * 递归计算，输入n，按规则计算n-1的序列
 */
public class CountAndSay {

    /**
     * 38-题目描述
     * https://leetcode.com/problems/count-and-say/
     *
     * @param n
     * @return
     */
    public static String countAndSay(int n) {
        String s = "1";
        for(int i = 1; i < n; i++) {
            //递归分解，n=n-1序列，n-1=n-2序列
            s=say(s);
        }
        return s;
    }

    public static String say(String s) {
        StringBuilder sb = new StringBuilder();
        for(int i = 0; i < s.length(); i++) {
            int count = 1;
            while( i+1