【一天一道LeetCode】#38. Count and Say

一天一道LeetCode系列

（一）题目

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.

（二）解题

/*
首先初始化字符串为1，对应一个1，读成11
字符串更新为11，对应两个1，读成21
字符串更新为21，对应1个2一个1，读成1211
....
依次进行n次则得到最后的字符串
*/
class Solution {
public:
    string countAndSay(int n) {
        string str = "1";
        while(--n)
        {
            string ret;
            for (int i = 0; i < str.length(); ) {
                int count = 0;
                while (i < str.length() && str[i] == str[i + 1]) {
                    count++;
                    i++;
                }
                ret += ('1' + count);
                ret += str[i];
                i++;
            }
            str = ret;
        }
        return str;
    }
};