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.

string countAndSay(int n) 
{	
	if(n == 1)
		return "1";

	string str = "1";
	string res = "";

	//把n个序列逐个求解
	for(int i=1; i<=n; ++i)
	{
		for(int j=0; j<str.length(); )
		{
			int count = 0;
			char c = str[j];
			//判断一个字符连续出现的次数count
			while(j<str.length() && c==str[j])
			{
				count++;
				j++;
			}
			
			//将出现的个数count和字符进行组合成字符串
			char tmp[3] = {0};
			tmp[0] = count + '0';
			tmp[1] = c;
			tmp[2] = '\0';
			
			res.append(tmp);

		}

		if(i == n-1)
			return res;
//		cout<<res<<endl;
		str = res;
		res = "";
	}

}