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Symmetrical Date Golf

by ryan (Pilgrim)
on Feb 28, 2002 at 13:38 UTC ( #148210=perlmeditation: print w/ replies, xml ) Need Help??

With the recent passing of a 'symmetrical date' (20:02 20/02 2002) and my inability to find any related posts on here, I present the following code from a co-member of a local linux users' group to produce a list of all symmetrical dates of the form HH:MM DD/MM YYYY

By symmetrical I mean either of the following examples:
  • overall symmetry: 16:12 30/03 2161
  • component and overall symmetry: 20:02 20:02 2002
We are in Australia, so we put dates in the form DD/MM .. assuming we can start with (00:00 10/01 0000) and end with (19:59 21/12 9591) - the code below produces 8640 such dates.

I'm simply curious to see the results of a few rounds of golf on this problem.
#!/usr/bin/perl -w my %symmetrical = (); my $time; my $year; my @months = ('1001', '2002', '3003', '0110', '1111', '2112'); foreach my $i (0 .. 2359) { $i = &fill($i); $i =~ m/(\d\d)(\d\d)/; if (($1 > 23) or ($2 > 59)) { next; } $time = $i; $year = reverse($i); $symmetrical{$year} = $time; } for my $i (sort(keys %symmetrical)) { my $ryear = $i; my $rtime = $symmetrical{$i}; $rtime =~ s/(\d\d)(\d\d)/$1:$2/; for my $rmonth (@months) { $rmonth =~ s/(\d\d)(\d\d)/$1\/$2/; print "$rtime\t$rmonth\t$ryear\n"; } } sub fill { my $i = shift; while (length($i) < 4) { $i = '0' . $i; } return $i; }

Comment on Symmetrical Date Golf
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147 Chars - Re: Symmetrical Date Golf
by metadoktor (Hermit) on Feb 28, 2002 at 14:54 UTC
    A first shot though I only generated 7198 variations...I must've done something wrong or misinterpreted something in your problem statement.
    #!/usr/bin/perl -w use strict; symdate(); sub symdate{ my($h,$n,$d,$m,$y,$r);my@x=qw(1001 2002 3003 0110 1111 2112);for('0000 +10'..'195921'){$r=reverse$_;$h=substr($_,0,2);$n=substr($_,2,2);$d=su +bstr($_,4,2);$m=substr($r,0,2);$y=substr($r,2,4);for(@x){if($_ eq $d. +$m){if(($h>=0)&&($h<24)&&($n>=0)&&($n<60)){print "$h:$n $d/$m $y\n";} +}}} }
    Update:

    Fixed the logical error and shortened the code down to 179 chars.

    sub symdate { my($f,$r);for('000000'..'235930'){$f=$_.reverse;$r='(..)'x6;$f=~s/$r/$ +1:$2 $3\/$4 $5$6/g;for(qw(1001 2002 3003 0110 1111 2112)){if(( $_ eq $3.$4)&&($1<24)&&($2<60)){print"$f\n";}}} }
    Update2:

    Shortened it down to 147 chars though still not as good as chipmunk's. Btw, it generates 8,640 solutions.

    sub symdate { for(qw(01 10 20 30 11 21)){for$h('00'..'23'){for$m('00'..'59'){$s="$h$ +m$_";$r='(..)'x6;$f=$s.reverse$s;$f=~s/$r/$1:$2 $3\/$4 $5$6/;print$f, +"\n";}}} }

    metadoktor

    "The doktor is in."

Re: Symmetrical Date Golf
by dragonchild (Archbishop) on Feb 28, 2002 at 15:34 UTC
    Two solutions.
    # This is 165 characters for(grep{/(..)(..)/;$1<24&&$2<60}map{sprintf"%04d",$_}0..2359){($t=$_) +=~s/(..)(..)/$1:$2/;$y=reverse;print map{"$t\t$_\t$y\n"}qw(10/01 20/0 +2 30/03 01/10 11/11 21/12)} ---- # This is 164 characters map{($t=$_)=~s/(..)(..)/$1:$2/;$y=reverse;print map{"$t\t$_\t$y\n"}qw( +10/01 20/02 30/03 01/10 11/11 21/12)}grep{/(..)(..)/;$1<24&&$2<60}map +{sprintf"%04d",$_}0..2359
    Update: Changed || to && as per metadoktor's note. This fixes the bug found.

    ------
    We are the carpenters and bricklayers of the Information Age.

    Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.

      I think your solutions are incomplete. They generate dates like this:
      00:90 20/02 0900
      which aren't valid since there aren't 90 minutes in an hour. ryan claims that there are 8640 solutions. I got a different number though...

      metadoktor

      "The doktor is in."

Re: Symmetrical Date Golf
by Anonymous Monk on Mar 01, 2002 at 00:44 UTC
    Ryan-

    I got a chain letter two weeks back that claimed that 20:02 20/02 2002 was a miraculous phenomenon that has only happened once before and won't ever happen again... not sure whether they meant simply the date being a palindrome or, more likely, the fact that the date can be split by whitespace in 3 identical palindromes. Well, I didn't believe it, so i wrote this script:

    http://www.parseerror.com/perl/date_palindrome.pl
    http://www.parseerror.com/perl/date_palindrome.txt (in case your browser doesn't like .pl files)

    Which finds a total of 1164 palindromes between 1001-3003 AD. Of these, 4 turn out to be the "three identical palindromes"...

    10:01 10/01 1001
    11:11 11/11 1111
    20:02 20/02 2002
    21:12 21/12 2112

    Anywho, all my results are included in the file and the source code is alot shorter and simpler than what you have, though it does take a while for the script to chug through all the dates from 1001-3003 AD.

    Hope someone finds this interesting... i figured i could do it with a one-liner, but was suprirsed to find out how complex this actual problem was.

    ryan aka pizza_milkshake
      Yes, I got that email too. It wrongly claimed that this event would NEVER happen again, when infact 21:12 21/12 2112 will occur in the future ... maybe not in our lifetime though :)

      It also did not explicitely specify that each component had to be symmetrical, that was at best only implied ... hence our broader interpretation of the problem.

      Thanks for the linkage.
Re: Symmetrical Date Golf
by chipmunk (Parson) on Mar 01, 2002 at 03:45 UTC
    I also found 8640 matches.

    This solution is 96 characters, although it orders the results by hour and minute, rather than by year. for$h('00'..'23'){for$m('00'..'59'){print"$h:$m $_/".reverse"\n$h$m $_"for 10,20,30,'01',11,21}}
    Or, by not worrying about a meaningful order to the results, I can get to 94: for$h('00'..'23'){for$M(102030011121=~/../g){print"$h:$_ $M".reverse"\n$h$_ $M"for'00'..'59'}}

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