Count and Say

Count and Say

问题：

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.

思路：

　　简单的数学推导而已

我的代码：

public class Solution {
    public String countAndSay(int n) {
        if(n <= 0)  return "";
        String rst = "1";
        for(int i = 1; i < n; i++)
        {
            String tmp = "";
            int len = rst.length();
            for(int j = 0; j < len; j++)
            {
                int count = 1;
                while(j < len-1 && rst.charAt(j) == rst.charAt(j+1))
                {
                    count++;
                    j++;
                }
                tmp += String.valueOf(count) + String.valueOf(rst.charAt(j));
            }
            rst = tmp;
        }
        return rst;
    }
}

学习之处：

• int char String相互转化方法  String.valueOf  Integer.valueOf Character.valueOf