package Schedule::RoundRobin;
###############################################################################
# implements a round robin scheduling algorithm as described in
# http://forum.swarthmore.edu/dr.math/problems/kinley.3.31.00.html
###############################################################################
# takes an array and returns a reference to a list of pairs
sub schedule
{
my(@teams) = @_;
# get the size of the array
my $size = scalar @teams;
# If it is even, pop off one item and maintain it as a central point
# and proceed as with an odd number
return undef unless ($size > 0);
my $pivot = undef;
my $even = 0;
my $end_point_a = 0;
my $end_point_b = $size-1;
if($size%2 == 0)
{
# $pivot = pop @teams;
$pivot = $#teams;
$even = 1;
$end_point_b--;
}
# Create a list of the "stripes" of the polygon, the stripes will be
# pairs of indices into the array
my @stripes;
# Assume that each element in the array is a vertex of the polygon
# and the vertices are listed in order, stripes are created
for (1..int(($size-1)/2))
{
push(@stripes, [$end_point_a, $end_point_b]);
$end_point_a++;
$end_point_b--;
}
# Upon falling out of the loop, the middle point will be in both
# end_point_a and end_point_b
if($even)
{
push(@stripes, [$end_point_a, $pivot]);
}
# Each element of the games array is a play date's worth of games
# so it is an array of pairs
my @games;
for(1..($size-$even))
{
my @this_week;
# push the weeks worth of games onto @games
foreach my $sched_ref (@stripes)
{
push (@this_week, [$teams[$sched_ref->[0]], $teams[$sched_ref->[1]]]);
}
push(@games, \@this_week);
# Now rotate the @teams array
my $last_team_save = undef;
# Save the last team as the pivot for the polygon
if($even)
{
$last_team_save = pop(@teams);
}
my $last_team = pop(@teams);
unshift(@teams, $last_team);
if($even)
{
push(@teams, $last_team_save);
}
}
return \@games;
}
1;