LeetCode Online Judge 题目C# 练习 - 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 n^th sequence.

Note: The sequence of integers will be represented as a string.

public static string CountandSay(int n)
        {
            string[] str = new string[2]; //两个 string 交替
            str[0] = "1"; //初始值
            int new_index = 0;
            int curr_index = 0;

            for (int i = 2; i <= n; i++)
            {
                new_index = (curr_index + 1) % 2; //交替index
                str[new_index] = ""; 
                char ch = str[curr_index][0];
                int num = 1; //counter
                for (int j = 1; j < str[curr_index].Length; j++)//循环str[curr_index]中每一个character
                {
                    if (str[curr_index][j] == ch) //相同character， num++
                        num++;
                    else
                    {
                        str[new_index] += num.ToString() + ch.ToString();
                        ch = str[curr_index][j]; 
                        num = 1;
                    }
                }

                str[new_index] += num.ToString() + ch.ToString();

                curr_index = new_index;
            }

            return str[new_index];
        }

代码分析：

　　有点太简单的说。注意循环之后的一个写入不要漏掉。