use strict;
use warnings;
use Benchmark qw(cmpthese);

sub algorithm {
    my $ref = shift;
    return (undef,undef,undef) if ! $ref;
    my @ary = @$ref;
    my ( $min, $max, $tot );
    
    if (@ary % 2) {
        $min = $max = $tot = shift( @ary );
    }
    else {
        ($min, $max) = ($ary[0] < $ary[1])
                     ? ($ary[0], $ary[1])
                     : ($ary[1], $ary[0]);
        $tot = $min + $max;
        splice( @ary, 0, 2 );
    }

    while ( @ary ) {
        if ( $ary[0] < $ary[1] ) {
            $min = $ary[0] if ( $ary[0] < $min );
            $max = $ary[1] if ( $ary[1] > $max );
        }
        else {
            $min = $ary[1] if ( $ary[1] < $min );
            $max = $ary[0] if ( $ary[0] > $max );
        }
        $tot += $ary[0] + $ary[1];
        splice( @ary, 0, 2 );
    }
    return ( $min, $max, $tot / @$ref );
}

sub simple {
  my $r = shift;
  
  if (@$r) {
    my ($min, $max, $tot) = ($r->[0]) x 3;
    for (@$r[ 1 .. $#{$r}]) {
      $min = $_ if $_ < $min;
      $max = $_ if $_ > $max;
      $tot += $_;
    }
    return ($min, $max, $tot / @$r);
  }
  return (undef, undef, undef)
}

my @nums = map { rand } ( 1 .. 1000 );

# verify they do the same thing!
# print "simple:      @{[simple(\@nums)]}\n";
# print "algorithm:   @{[algorithm(\@nums)]}\n";

cmpthese(-1, { algorithm => sub { my @r = algorithm(\@nums) },
           simple => sub { my @r = simple(\@nums) } })
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