At home my daughter has a little “spy” safe where she can keep money, rocks, or whatever else she wants in there. This safe is guarded by a passcode, and when you enter the passcode incorrectly twice it makes an alarm sound. Real cute.

I am always stopping by when she’s trying to do something and guess the passcode, annoying her with the alarm sound. Last night it occurred to me to write a quick little program to display all possible combinations for the passcode. So I did. With digits 1, 2, 3, and 4 there are 256 possible combinations.

package com.adampresley.NumDigits;

public class Main
{
   public static void main(String[] args) {
      go("1234", 4, new StringBuffer());
   }

   static void go(String input, int depth, StringBuffer output) {
      if (depth == 0) {
         System.out.println(output);
      } 
      else {
         for (int i = 0; i < input.length(); i++) {
            output.append(input.charAt(i));
            go(input, depth - 1, output);
            output.deleteCharAt(output.length() - 1);
         }
      }
   }
}

After 15 tries my fiancee gets tired of the noise it’s making and has my daughter come take the safe away from me. My daughter then tells me the actual combination. Social engineering at it’s finest!

Happy coding!