leetcode-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.

思路：递归

代码：

string countAndSay(int n) {
    string res;


if(n<1)
return NULL;
else if(n == 1)
{
res="1";
return res;
}
else if(n == 2)
{
return "11";
}
int lenOfRes=0;
string s=countAndSay(n-1);
int len=s.length();
int count=1;
char temp;

int i=0;
for(i=0; i<len-1; ++i)
{
if(s[i] == s[i+1])
{
count++;
}
else
{
   temp=count+48;
res+=temp;
res+=s[i];
count=1;
}
}
if(s[i-1] == s[i])
{
   temp=count+48;
res+=temp;
res+=s[i];
}




if(s[i-1] != s[i])
{
   temp=49;
res+=temp;
res+=s[i];
}


return res;
    }