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 countAndSay(int n) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
string str = "1";
for (int i = 1; i < n; ++i)
{
string tmp;

int count = 1;
char ch = str[0];
for (int j = 1; j < str.size(); ++j)
{
if (str[j] == ch)
++count;
else
{
tmp.insert(tmp.end(), char(count+'0'));
tmp.insert(tmp.end(), ch);
ch = str[j];
count = 1;
}
}
tmp.insert(tmp.end(), char(count+'0'));
tmp.insert(tmp.end(), ch);
str = tmp;
}
return str;
}
};