Count and Say 

The count-and-say sequence is the sequence of integers beginning as follows:
1, 11, 21, 1211, 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 sequence.

Note: The sequence of integers will be represented as a string.

思路：題意實在太難理解了，尤其是英文又不好，只能參看下別人的資料，理解下規則。終於理解，題意是n=1時輸出字串1；n=2時，數上次字串中的數值個數，因為上次字串有1個1，所以輸出11；n=3時，由於上次字元是11，有2個1，所以輸出21；n=4時，由於上次字串是21，有1個2和1個1，所以輸出1211。依次類推，寫個countAndSay(n)函式返回字串。

題意理解之後就好辦了，是典型的遞迴問題，其程式碼很簡單，如下：

public class Solution {
    public String countAndSay(int n) {
        if(n == 1){
            return "1";
        }
        //遞迴呼叫，然後對字串處理
        String str = countAndSay(n-1) + "*";//為了str末尾的標記，方便迴圈讀數
        char[] c = str.toCharArray();
        int count = 1;
        String s = "";
        for(int i = 0; i < c.length - 1;i++){
        	if(c[i] == c[i+1]){
        		count++;//計數增加
        	}else{
        		s = s + count + c[i];//上面的*標記這裡方便統一處理
        		count = 1;//初始化
        	}
        }
        return s;
    }
}