題目：

The count-and-say sequence is the sequence of integers with the first five terms as following:

1.     1
2.     11
3.     21
4.     1211
5.     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"

Given an integer n where 1 ≤ n ≤ 30, generate the nth term of the count-and-say sequence.

Note: Each term of the sequence of integers will be represented as a string.

Example 1:

Input: 1
Output: "1"

Example 2:

Input: 4
Output: "1211"

程式碼：

class Solution {
public:
    string countAndSay(int n) {
        if (n < 1 || n>30) return "";
	if (n == 1)return "1";
	string last = countAndSay(n - 1);
	char c='.';
	string res = "";int count = 0;
	for (int i = 0; i < last.length(); i++) {
		
		if (c != last[i]) {
			if (count != 0) {
				string s1 = to_string(count);
				s1.push_back(c);
				res += s1 ;
		   }
			c = last[i];
			count = 1;
		}
		else count++;
	}

	
	string s1 = to_string(count);
	s1.push_back(c);
	res += s1 ;
	return res;
    }
};
 

注：

1、使用遞迴的思路求解

2、學會不同型別之間的轉換：int 轉為 string---to_string()，char轉為string---s.push_back()