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：题目很简单，看清题意，代码如下：

class Solution {public:      string countAndSayOnce(string s){        string ret = "";        int i = 0, len = s.length();        while(i++ < len){            int count = 1;            while(i < len && s[i] == s[i - 1]){                count ++;                i++;            }            ret += count + '0';            ret += s[i - 1];        }        return ret;    }     string countAndSay(int n) {        string s = "1";        for(int i = 0; i < n - 1; ++i)            s = countAndSayOnce(s);        return s;     }};