LeetCode_38. Count and Say

38. Count and Say

Easy

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 where 1 ≤ n ≤ 30, generate the nth term of the count-and-say sequence.

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

Example 1:

Input: 1
Output: "1"

Example 2:

Input: 4
Output: "1211"

package leetcode.easy;

public class CountAndSay {
	@org.junit.Test
	public void test() {
		for (int i = 1; i <= 4; i++) {
			System.out.println(countAndSay(i));
		}
	}

	public String countAndSay(int n) {
		String str = "1";
		for (int i = 1; i < n; i++) {
			str = countID(str);
		}
		return str;
	}

	private static String countID(String str) {
		// TODO Auto-generated method stub
		StringBuffer buffer = new StringBuffer();
		char c = str.charAt(0);
		int count = 1;
		for (int i = 1; i < str.length(); i++) {
			if (str.charAt(i) == c) {
				count++;
			} else {
				buffer.append(count);
				buffer.append(c);
				c = str.charAt(i);
				count = 1;
			}
		}
		buffer.append(count);
		buffer.append(c);
		return buffer.toString();
	}
}