leetcode--Count and Say

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.

[java]  view plain  copy

1. public class Solution {  
2.     public String countAndSay(int n) {  
3.         if(n<1) return "";  
4.         String str = "1";  
5.         while(--n>0){  
6.             StringBuilder sb = new StringBuilder();           
7.             char[] arr = str.toCharArray();  
8.             char pre = arr[0];  
9.             int count = 1;  
10.             for(int i=1;i<arr.length;i++){  
11.                 if(pre!=arr[i]){                          
12.                     sb.append(count).append(pre);  
13.                     count = 1;  
14.                     pre = arr[i];         
15.                 }else{  
16.                     count++;  
17.                 }  
18.             }  
19.             sb.append(count).append(pre);    
20.             str = sb.toString();  
21.         }                 
22.         return str;  
23.     }  
24. }  

原文链接http://blog.youkuaiyun.com/crazy__chen/article/details/45696665