Count and Say-LeetCode

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.

用到了一个平时没有用到的stringstream，用来将int转化为string，十分便捷，使用方法见下面的博文链接。

http://www.cppblog.com/Sandywin/archive/2007/07/13/27984.html

代码：

class Solution {
public:
    string getnextstr(string str)
    {
    	stringstream ss;
    	char key =  str[0];
     	char current = str[0];
    	int count = 0;

    	for (int i = 0; i < str.length(); i++)
    	{
    		current = str[i];
    		if (key == current)
    		{
    			count++;
     			
	    	}
    		else
    		{
	    		ss<<count<<key;
	    		key = current;
	    		count = 1;
	    	}
    	}
    	ss<<count<<key;
    	return ss.str();
    }

    string countAndSay(int n) {
    	string result = "1";
    	if ( n <= 0)
    	{
    		return NULL;
    	}
    	if (n == 1)
      	{	
	    	return result;
    	}
    	for (int i = 0; i < n - 1; i++)
    	{
    		result = getnextstr(result);
    	}
    	return result;

    }
};