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"

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.

這個題目的意思就是此時的字串由上一個字串來定義，也就是count+say，程式碼如下：

class Solution {
    public String countAndSay(int n) {
        StringBuffer cur = new StringBuffer("1");
        StringBuffer prev;
        int count = 0;
        char say;
        for(int i = 1 ; i < n ; i++){
            prev = cur;
            cur = new StringBuffer();
            count = 1;
            say = prev.charAt(0);
            for(int j = 1,len = prev.length() ; j < len;j++){
                if(prev.charAt(j) != say){
                    cur.append(count).append(say);
                    count = 1;
                    say = prev.charAt(j);
                }else{
                    count++;
                }
            }
            cur.append(count).append(say);
        }
        return cur.toString();
    }
}