Count and Say

题目描述：

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.

AC代码如下：

class Solution {
public:
string countAndSay(int n) {
string ans = "1";
if (n <= 0) return string();
for (int i = 0; i < n - 1; i++){
int length = ans.size();
string tmp = "";
int count = 1;
for (int j = 1; j < length; j++){
if (ans[j] == ans[j - 1]){
count++;
}
else{
char ch = ans[j - 1];
char cc = '0' + count;
tmp = tmp + cc + ch;
count = 1;
}
}
char ch = ans[length - 1];
char cc = '0' + count;
tmp = tmp + cc + ch;
ans = tmp;
}
return ans;
}
};