题目：

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：

题目理解比较费时，就是一个常规的递归问题。

代码：

class Solution {
public:
    string countAndSay(int n) {
        if(n==1)
        {
            return "1";
        }
        else if(n==2)
        {
            return "11";
        }
        else
        {
            string str = countAndSay(n-1);
            string result;
            int pre;
            int cur=str[0]-'0';
            int count=1;
            for(int i=1;i<str.size();i++)
            {
                pre=cur;
                cur=str[i]-'0';
                if(pre==cur)
                {
                    count++;
                }
                else
                {
                    result.push_back(count+'0');
                    result.push_back(pre+'0');
                    count=1;
                }
            }
            result.push_back(count+'0');
            result.push_back(cur+'0');
            return result;
        }
    }
};