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);
};

string Solution::countAndSay(int n)
{
string b = "";
if(n == 1) return "1";
if(n == 2) return "11";
string s = "11";
//ong long  num = 2;
for(int i = 2; i < n; i++)   //变化次数就是 n-1；
{
for(int j = 0; j < s.size();4)
{ int k = j+1;
while (k < s.size() && s[k] == s[j]) {
k++;
}
b += (k - j + '0');
b += s[j];
j = k;
}

s = b;
b = "";
}
return s;
}