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.
11is read off as "two 1s" or 21.
21is read off as "one 2, then one 1" or 1211.
Given an integer n, generate the nth sequence.

My solution:

public class Solution {
   /**
    * @param n the nth
    * @return the nth sequence
    */
   public String countAndSay(int n) {
       // Write your code here
       String str = “”;
       if (n == 1)
           return “1”;
       str = 1 + str;

       int i = 1;
       int len;

       while (i < n) {
           str = helper(str);
           i++;
       }

       return str;
   }

   public String helper(String str) {
       String ret = “”;
       int len = str.length();
       int i = 0;
       while (i < len) {
           char a = str.charAt(i);
           int count = 0;

           while (i < len && str.charAt(i) == a) {
               i++;
               count++;
           }
           ret =  ret + count + “” + a;

       }
       return ret;
   }
}

Solution 2

public class Solution {
    /**
     * @param n the nth
     * @return the nth sequence
     */
    public String countAndSay(int n) {
        // Write your code here
        String oldString = "1";
        while (--n > 0) {
            StringBuilder sb = new StringBuilder();
            char [] oldChars = oldString.toCharArray();

            for (int i = 0; i < oldChars.length; i++) {
                int count = 1;
                while ((i+1) < oldChars.length && oldChars[i] == oldChars[i+1]) {
                    count++;
                    i++;
                }
                sb.append(String.valueOf(count) + String.valueOf(oldChars[i]));
            }
            oldString = sb.toString();
        }

        return oldString;
    }
    
    
}