[leetcode] 38. Count and Say 解题报告

题目链接：https://leetcode.com/problems/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.

思路：本题的意思是用一个计数＋字符来编码一个数字，接着再用计数＋字符编码上一个结果，这样会形成一个序列。最后将结果保存到字符串中。

代码如下：

class Solution {
public:
    string countAndSay(int n) {
        string str = "1";
        while(--n)
        {
            string tem;
            int i = -1, cnt = 0;
            char ch = str[0];
            while(++i < str.size())
            {
                if(str[i] == ch) cnt++;
                else
                {
                    tem += to_string(cnt) + ch;
                    cnt = 1;
                    ch = str[i];
                }
            }
            tem += to_string(cnt) + ch;
            str = tem;
        }
        return str;
    }
};