Round Robin Tournament playoff scheduler wanted

[John P. Nelson]

>Given a list of the names of the players in a tournament (such
>as golf or chess) I'd like sources to a program which calculates
>the number of rounds required and the pairs of players scheduled
>to play during each round.
>
>CONDITIONS:
>-   Every player must play every other player exactly once.
>-   Every player must have an opponent during every round.

I took a shot at this, and implemented it using "perl".  Depending on
how you invoke perl on your system, you may need to modify the first
few lines of this script.

#! /usr/local/perl
# roundrobin - take a list of player names, and create a roundrobin
#              tournament where each player plays every other player
#              exactly once, and each player is active each round.

# collect the names, one per line.
$maxlen = 0;
$phantom = "__phantom__";
while (<>) {
    chop;
    push(players, $_);
    if (length > $maxlen) { $maxlen = length; }
}

die "Note enough players" if ($#players < 2);
$format = sprintf("%%-%ds plays %%%ds\n", $maxlen, $maxlen);

# make sure we have an even number of players.
if (($#players & 1) == 0) {
    unshift(players, $phantom);
}

# make rotator with two arrays and a pivot
$pivot = $players[0];
@list1 = @players[1..(($#players-1)/2)];
@list2 = @players[(($#players+1)/2)..$#players];

# perform the round robin
for ($i = 1; $i <= $#players; ++$i) {
    print "\n Round $i:\n";
    if ($pivot eq $phantom) { print "$list2[0] is idle\n"; }
    else { printf $format, $pivot, $list2[0]; }

    for ($j = 0; $j <= $#list1; ++$j) {
	printf $format, $list1[$j], $list2[$j+1];
    }
    # rotate the players
    $temp = shift(list2);
    unshift(list1, $temp);
    $temp = pop(list1);
    push(list2, $temp);
}

---
     john nelson

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