Count and Say.java

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.

public class Solution {
    public String countAndSay(int n) {
        StringBuilder s1 = new StringBuilder("1");
        StringBuilder s2 = new StringBuilder();
        for (int i = 1; i < n; i++) {
            int j = 0;
            int len = s1.length();
            while (j < len) {
                int count = 1;
                char c = s1.charAt(j);
                while (j < len - 1 && s1.charAt(j + 1) == s1.charAt(j)) {
                    count++;
                    j++;
                }
                s2.append(count + "");
                s2.append(c);
                if (j == len - 1) {
                    break;
                }
                j++;
            }
            s1 = s2;
            s2 = new StringBuilder();
        }
        return s1.toString();
    }
}