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 nth sequence.

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

class Solution {
public:
string itos(int n) {

if (n <= 0)
return "";

string retStr = "";
while(n > 0)
{
retStr += n%10 + '0';
n = n/10;
}

return retStr;
}

string countAndSay(int n) {

if (n <= 0)
return "";

int count = 1;
string curStr = "1";
string nextStr;

while (count < n)
{
int len = curStr.size();

char preChar = curStr[0];
char curChar;
int  charCount = 1;
for (int i=1; i<len; i++)
{
curChar = curStr[i];
if (curChar == preChar)
{
charCount++;
}
else
{
nextStr += itos(charCount);
nextStr += curStr[i-1];

charCount = 1;
preChar = curStr[i];
}
}

nextStr += itos(charCount);
nextStr += preChar;

curStr = nextStr;
nextStr = "";

count++;
}

return curStr;
}
};