Java [leetcode 38]Count and Say

题目描述：

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.

解题思路：

从第一个开始数起，对于输入n，则数n-1次即可。

代码如下：

public class Solution {
    public String countAndSay(int n) {
		int i = 1;
		if (n <= 0)
			return null;
		String s = "1";
		while (i <= n - 1) {
			s = countAndSay(s);
			i++;
		}
		return s;
	}

	public String countAndSay(String s) {
		int count = 1;
		StringBuffer sb = new StringBuffer();
		for (int i = 1; i < s.length(); i++) {
			if (s.charAt(i - 1) == s.charAt(i))
				count++;
			else {
				sb.append(count).append(s.charAt(i - 1));
				count = 1;
			}
		}
		sb.append(count).append(s.charAt(s.length() - 1));
		return sb.toString();
	}
}