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.

n=1时，输出字符串为1

n=2时，输出字符串为11(表示前一个字符串中有1个1)

n=3时，输出字符串为21（表示前一个字符串中有2个1）

n=4时，输出字符串为1211（表示前一个字符串中有1个2,1个1）

....

可以发现输出结果是前一个字符串的各个数字字符的个数（个数+字符）

class Solution {
public:
string countAndSay(int n) {
string tmp="1";
for(int i=1;i<n;i++)
{
string stmp="";
for(int j=0;j<tmp.size();j++)
{
int k=j+1;
while(k<tmp.size()&&tmp[j]==tmp[k]) k++;
stringstream stream;
stream<<(k-j);
string ss;
stream>>ss;
stmp+=ss;
stmp+=tmp[j];
j=k-1;
}
tmp=stmp;
}
return tmp;
}
};