LeetCode38. Count and Say

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" or 1211.

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

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

思路

寫一個遞歸就是咯、讀取當前的String，即形成新的String。

代碼

public class Solution {

	//子函數，讀取當前的String形成新的String
    public String countAndSay_Sub (String s){
		String result = "";
		int count = 1;
		int i = 0;
		while(i < s.length()){
			while((i + count) < s.length() && s.charAt(i) == s.charAt(i + count))	++ count;
			result = result + count + s.charAt(i);
			i = i + count;
			count = 1;
		}
		return result;
	}
    public String countAndSay(int n) {
        String result = "1";
        for(int i = 1 ; i < n ; ++ i){
            result = countAndSay_Sub(result);
        }
        return result;
    }
}