问题描述：

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" or11.
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.

代码：

public class Count_and_Say {  //java

	public String countAndSay(int n) {
        if(n < 1) return "";
        if(n == 1) return "1";
		
		String result = "1";
		for(int i = 2; i <=n; i++){
			result = generateStr(result);
		}
		return result;
    }
	
	public String generateStr(String s){
		String tmp = "";
		int count = 1;
		char ch = s.charAt(0);
		for(int i = 1; i<s.length(); i++){
			if(ch == s.charAt(i))
				count++;
			else{
				tmp += count +""+ ch;
				count = 1;
				ch = s.charAt(i);
			}
		}
		tmp += count + "" +ch;  // can't ignore the "";
		return tmp;
	}
	
	
	public static void main(String [] args){
		Count_and_Say cas = new Count_and_Say();
		System.out.println(cas.countAndSay(4));
		
	}
}

[leetcode]Count and Say