[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.

思考：有点斐波拉契的意思，一步一步求得字符串。

class Solution {
public:
    string countAndSay(int n) {
        string str="1";
		if(n==1) return str;
		
		int k=0;
		int i,j;
		for(i=1;i<n;i++)
		{
			string ans="";
			int pos=0;
			char ch=str[0];
			int len=str.size();
			for(j=1;j<=len;j++)
			{
				if(str[j]!=ch||j==len)
				{
					ans+=char((j-pos)+'0');
					ans+=ch;
					pos=j;
					if(j!=len) ch=str[j];
					else break;
				}
			}
			str=ans;
		}
		return str;
    }
};