Consider a date formatted in YYYY-MM-DD. You can use the joker * at the end of the date string. E.g. 2016-07-2* describes all the dates from 2016-07-20 to 2016-07-29.

Now, consider a period represented by a start date and an end date.

The algorithm must find the smallest possible list of dates representing the period.

Let's use an exemple. For the following period:

  • start date: 2014-11-29
  • end date: 2016-10-13

The algorithm must return an array containing the following list of dates:

  • 2014-11-29
  • 2014-11-30
  • 2014-12-*
  • 2015-*
  • 2016-0*
  • 2016-10-0*
  • 2016-10-10
  • 2016-10-11
  • 2016-10-12
  • 2016-10-13
  • 1
    \$\begingroup\$ The winning objective(s) are ambiguous. I suggest changing it to codegolf (i.e. solve the task in the fewest bytes possible) and always require answers to output the smallest list of dates. \$\endgroup\$
    – Billywob
    Commented Nov 9, 2016 at 10:22
  • \$\begingroup\$ Maybe it's simply not the best site for this, it is more a question (i.e. "I can't find this algorithm in Ruby on Rails") than a challenge "for fun". I'm rather new here... \$\endgroup\$
    – Raphael
    Commented Nov 9, 2016 at 10:28
  • \$\begingroup\$ I suggest you try stackoverflow and then ask it as a question rather than a challenge. If rephrased, the challenge is still interesting in my opinion and deserves a chance (as code golf). \$\endgroup\$
    – Billywob
    Commented Nov 9, 2016 at 10:36
  • 6
    \$\begingroup\$ Yeah, I think finding the algorithm is still fun and challenging, but I was not interested in the code-golf side... Well I rephrased it, changed the tags, and now I'm gonna ask stackoverflow while still following this post. Thanks! \$\endgroup\$
    – Raphael
    Commented Nov 9, 2016 at 10:39
  • 1
    \$\begingroup\$ Follow-up: I posted on Stackoverflow yesterday, but today I had a working code in Ruby (it doesn't "jokerize" months, but almost there): stackoverflow.com/questions/40506639/… \$\endgroup\$
    – Raphael
    Commented Nov 10, 2016 at 17:19

1 Answer 1


PHP, 541 343 bytes

I wanted to get the algorithm working in the first place; but golfing it down was actually far more fun than I expected (especially browsing the supported date & time formats).

Three major actions saved about 130 bytes; but the 70 bytes from minor golfings
(which also rendered one of the large steps obsolete) carried a lot of fun.

for($a=($f=strtotime)($argv[1]);!$p=$a>$z=$f($argv[2]);$a+=86400){$x=$z<$e=$f(Dec31,$a);(101<$q=date(md,$a))?$q-1001|$x?:$a=$e+$p="1*":($x?($t=$f(IX30,$a))>$z?:$a=$t+$p="0*":$a=$e+$p="*");$p?:($q%100>1|$z<($t=$f(date(Ymt,$a)))?$q%10>0&$q%100>1|$z<($t=min($t,$a+777600))?:$a=$t+$p="m-$q[2]*":$a=$t+$p="m-*");echo date("Y-".($p?:"m-d"),$a),"

takes input from command line arguments. Run with -nror test it online.


  • prints Y-m-3* for Y-m-30; add 7 bytes to fix: Insert |$a==$t after 777600)).
  • throws warnings in PHP 7.1; add 5 bytes to fix: Replace +$p with +!$p.
  • A breakdown and some golfings explained are ready to be posted;
    but I´ll wait a bit to see if someone else submits before I spoil.

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