Count and Say:循环记录字符串中数字个数

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

1.     12.     113.     214.     12115.     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, 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: 1Output: "1"

Example 2:

Input: 4Output: "1211"

思路：这题不容易读明白，可以理解为：

At the beginning, I got confusions about what is the nth sequence. Well, my solution is accepted now, so I'm going to give some examples of nth sequence here. The following are sequence from n=1 to n=10:

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

From the examples you can see, the (i+1)th sequence is the "count and say" of the ith sequence!

即i=5时，从左往右扫描字符串4，发现有一个1，一个2，两个1，于是写作111221.

看懂样例，模拟就行。

class Solution {    public String countAndSay(int n) {        if(n<=0) return "";        String r = "1";        for(int i = 1;i<n;i++){            StringBuilder b = new StringBuilder();            int count = 1;            char t = r.charAt(0);            for(int j =1;j<r.length();j++){                if(r.charAt(j)==t){                    count++;                }else{                    b.append(count).append(t);                    t = r.charAt(j);                    count = 1;                }            }            b.append(count).append(t);            r = b.toString();            System.out.println(r);        }        return r;    }}