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.

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

原题链接：https://oj.leetcode.com/problems/count-and-say/

能够看出，后一个数字是前个数字的读法，21读作1个2，先写下12，1个1，再写下11，连起来1211.

	public static String countAndSay(int n) {

		if(n <= 0)

			return null;

		String str = "1";

		int count = 1;

		for(int i=0;i<n-1;i++){

			StringBuilder builder = new StringBuilder();

			for(int j=0;j<str.length();j++){

				if(j<str.length()-1 && str.charAt(j)==str.charAt(j+1))

					count++;

				else{

					builder.append(count + "" + str.charAt(j));

					count = 1;

				}

			}

			str = builder.toString();

		}

		return str;

	}