Re: Average start time handling midnight

[hippo]

Subtract 24h from all times which are >12:00. Then calculate the mean, which is an offset from midnight. If the mean is < 0, add 24h back onto it.

[GotToBTru]

Your algorithm has trouble with the first example, 11a and 1pm. Average of 11 and -11 is 0.

Update (and updated again - no need to test for negative average (and updated again to allow minutes along with hours)):

use strict;
use warnings;
use Test::Simple tests => 8;

ok(&avg('01:05','03:13') eq '02:09', 'AM Only');
ok(&avg('20:43','22:45') eq '21:44', 'PM Only');
ok(&avg('09:00','13:00') eq '11:00', 'AM to PM');
ok(&avg('15:12','01:52') eq '20:32', 'PM to AM next day');
ok(&avg('09:10','07:08') eq '20:09', 'AM to AM next day');
ok(&avg('15:02','13:30') eq '02:16', 'PM to PM next day');
ok(&avg('11:00','13:00') eq '12:00', 'OP Example 1');
ok(&avg('23:00','01:00') eq '00:00', 'OP Example 2');

sub avg {
  my ($x,$y) = @_;
  $x = ttoi($x);
  $y = ttoi($y);
  if ($y < $x) {
    $y += (24 * 60);
  }
  return itot((($x + $y)/2) % (24 * 60));
}

sub ttoi {
  my $t = shift;
  my ($h,$m) = split /:/,$t;
  return $h * 60 + $m;
}

sub itot {
  my $i=shift;
  my $h = $i / 60;
  my $m = $i % 60;
  return sprintf "%02d:%02d",$h,$m;
}

[hippo]

I had rather taken that first example to be an illustration of what chrisjej didn't want. Perhaps we need a better-defined spec?