public static String translateBack(String back) {
         StringBuilder builder=new StringBuilder(back); 
         String reverse = builder.reverse().toString();
         String result = "";
         for(int i=0; i<reverse.length();i++) {
                 Character a =  reverse.charAt(i);
                 if(a==' ') {
                         result += ' ';
                 } else if(a=='R') {
                         result += 'L';
                 } else if(a=='U') {
                         result += 'D';
                 } else if(a=='D') {
                         result += 'U';
                 } else if(a=='L') {
                         result += 'R';
                 } else {
                         // Should not enter here!
                 }
         }
        return result;
    }