Interview Question for Senior Software Engineer at Box:

This is simply the number of ways you can permute a string.

Simply pass in a boolean array that determines which letter of the string have been used and which haven't:

permuteStrings(String x, int currentIndex, boolean[] isUsed, char[] originalString) {
  if (currentIndex == originalString.length) {
     System.out.println(x);
  }

  else {
  for (int i = 0; i < originalString.length; i++) {
       if (isUsed[i]) {
           continue;
       } else {
             isUsed[i] = true;
             permuteStrings(new String(x.append(originalString[i])), currentIndex++, isUsed, originalString);
             isUsed[i] = false;
       }

  }

}
}