public class Solution {
  public static void main(String[] args) {
      String S1 = "ABCD";   //println
      //output char one by one from String S1 forward
      //sample output
      //A
      //B
      //C
      //D
      //output char one by one from Strign S1 backward
      //sample output
      //D
      //C
      //B
      //A
      String S2 = "EFGH";
      //output char one by one from S1 and S2
      //alternatively forward in the same line  (print)
      //sample output: AEBFCGDH

      //output char one by one from S1 and S2
      //alternatively backward in the same line  (print)
      //sample output: HDGCFBEA
      for (int i=0; i<S1.length(); i++){
        System.out.println(S1.charAt(i));
     }
     for (int i=S1.length()-1; i>=0; i--){
        System.out.println(S1.charAt(i));
     }
     for (int i=0; i<S1.length(); i++){
        System.out.print(S1.charAt(i));
        System.out.print(S2.charAt(i));
     }
     System.out.println();
     for (int i=S1.length()-1; i>=0; i--){
        System.out.print(S2.charAt(i));
        System.out.print(S1.charAt(i));
     }
     System.out.println();
      //Final
      //output char one by one from S1 and S2
      //S1  forward
      //S2  backward
      //alternatively in the same line  (print)
      //sample output: AHBGCFDE
     for (int i=0; i<S1.length(); i++){   //forward loop
        System.out.print(S1.charAt(i));
        System.out.print(S2.charAt(S1.length()-1-i));
        //last index-1   can get backward index
     }

    }
}