lintcode-easy-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 nth sequence.

Example

Given n = 5, return "111221".

Note

The sequence of integers will be represented as a string.

思路也很直接，但是写的时候要注意数组index越界一类的问题

public class Solution {
    /**
     * @param n the nth
     * @return the nth sequence
     */
    public String countAndSay(int n) {
        // Write your code here
        if(n < 1)
            return null;

        if(n == 1)
            return "1";

        String prev = "1";
        String next = "";

        for(int i = 2; i <= n; i++){
            char[] temp = prev.toCharArray();

            int index = 0;
            while(index < temp.length){
                int count = 0;

                count++;
                index++;
                while(index < temp.length && temp[index] == temp[index - 1]){
                    count++;
                    index++;
                }
                next = next + String.valueOf(count) + temp[index - 1];
            }
            prev = next;
            next = "";
        }

        return prev;
    }
}