For the question Find the highest unique digit , here is my answer :


At the end I am essentially trying to achieve a lastIndexOf. I do that by reversing my array, using indexOf, and subtracting from 9. This adds 4 (9 W % -) extra bytes to get from indexOf to lastIndexOf.

Furthermore, if I didn't know my array was length 10 the code would be even longer, and secondly, this code returns 10 when indexOf is -1 which may not be acceptable in many situations.

Any suggestions on a shorter way to do the lastIndexOf operation (generally or just as needed for this challenge)?

  • \$\begingroup\$ I want to ask the same thing, but in pyth :P \$\endgroup\$
    – Mr. Xcoder
    Jul 15, 2017 at 14:51
  • \$\begingroup\$ @EriktheOutgolfer Thanks, I changed it to shorter. And I'm interested in solutions for any of the cases: 1) my challenge 2) variable array length 3) -1 case. \$\endgroup\$
    – geokavel
    Jul 15, 2017 at 19:02
  • \$\begingroup\$ @geokavel OK, posting mine as an answer for 3) then. :) \$\endgroup\$ Jul 15, 2017 at 19:03

2 Answers 2


Splitting is sometimes a good way to do this. E.g.

e# Stack: ... haystack needle

With variants, such as removing the a if both needle and haystack are strings.

  • \$\begingroup\$ Golfed: a/)a*,. \$\endgroup\$
    – jimmy23013
    Jul 16, 2017 at 14:43
  • \$\begingroup\$ Note: doesn't handle -1 case. Outputs 0 instead. \$\endgroup\$
    – geokavel
    Jul 16, 2017 at 18:15

9 bytes


Try it online!

You must have ...element list exactly like this in the stack. If W doesn't contain -1 you must replace it with something that does evaluate to -1.

  • \$\begingroup\$ Note: doesn't handle -1 case. Outputs length of array instead. \$\endgroup\$
    – geokavel
    Jul 16, 2017 at 18:16
  • \$\begingroup\$ @geokavel Yeah the -1 case is being worked on... \$\endgroup\$ Jul 16, 2017 at 18:18
  • \$\begingroup\$ In the case where the array has a known length, outputting the length could sometimes be usable, since at least it is a unique value that could not be confused with a valid index. \$\endgroup\$
    – geokavel
    Jul 16, 2017 at 18:20

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