import java.util.ArrayList;

/**
   Encodes strings using the Railfence cipher.
*/
public class Railfence
{
    /**
       Arranges a message in a fence pattern
       @param message any string
       @return a two-dimensional array of strings that are either null (.) or strings
       of length 1, arranged in a pattern like this
       m . . . a . .
       . e . s . g .
       . . s . . . e
    */
    public String[][] makeFence(String message)
    {
       String[][] fence = new String[3][message.length()];

       for(int i = 0; i < message.length(); i++)
       {
          if(i % 4 == 0)
          {
             fence[0][i] = Character.toString(message.charAt(i));
             fence[1][i] = null;
             fence[2][i] = null;
          }

          else if(i % 2 == 0)
          {
            fence[0][i] = null;
            fence[1][i] = null;
            fence[2][i] = Character.toString(message.charAt(i));
          }

          else
          {
            fence[0][i] = null;
            fence[1][i] = Character.toString(message.charAt(i));
            fence[2][i] = null;
          }
       }
       return fence;
    }


    // This message is used to check your work
    public String encode(String message)
    {
       String[][] fence = makeFence(message);
       String result = "";
       for (int i = 0; i < fence.length; i++)
          for (int j = 0; j < fence[i].length; j++)
             if (fence[i][j] != null && fence[i][j].length() == 1)
                result = result + fence[i][j];
       return result;
    }
}