[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.

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;
}
};