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" or 1211.

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.

Example 1:

Input: 1
Output: "1"

Example 2:

Input: 4
Output: "1211"

递归解法

class Solution {
public:
    string countAndSay(int n) {
        if(n==1)
            return "1";
        string s=countAndSay(n-1),s2="";
        int len=s.length();
        for(int i=0;i<len;i++){
            int count=1;
            while(i<len-1&&s[i]==s[i+1]){
                count++;
                i++;
            }
            s2+=(count+'0');
            s2=s2+s[i];
        }
        return s2;
    }
};

非递归解法

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