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： 一个数字A连续出现N次，就读成”NA”，

实现如下：

class Solution {
public:
    string tostr(int c){
        string ret;
        stringstream ss;
        ss<<c;
        ret=ss.str();
        cout<<ret<<endl;
        return ret;
    }
    string ctostr(char c){
        string ret;
        stringstream ss;
        ss<<c;
        ret=ss.str();
        return ret;
    }
    string countAndSay(int n) {
        string s="1";
        for(int i=2;i<=n;i++){
            char last=‘A‘;
            int cnt=0;
            string r="";
            for(int j=0;j<s.length();j++){
                if(last==‘A‘){
                    last=s[j];
                    cnt=1;
                }else if(last==s[j]){
                    cnt++;
                }else{
                    r+=tostr(cnt);
                    r+=ctostr(last);

                    cnt=1;
                    last=s[j];
                }
            }
            r+=tostr(cnt);
            r+=ctostr(last);
            s=r;
        }
        return s;
    }
};