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 n^th sequence.

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

字符串處理一定要注意邊界和細節！

class Solution {
public:
    string covert(string s){
       char p = s[0];
       int cnt = 1;
       string ans;
       for(int i = 1; i <= s.size(); i++){
              if(s[i] == p)
                  cnt++;
              else {
                char tmp  = cnt + '0';
                ans =ans + tmp + p;
                cnt = 1;
                p = s[i];
              }
       }
       return ans;
    }
    string countAndSay(int n) {
        string ss = "1";
        for(int i = 1; i < n; i++)
            ss = covert(ss);
            return ss;      
    }
};