[leetcode]Count and Say

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"

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.

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));

}
}