Round Robin Algorithm

round_robin.php

<?php

/**
 * Rotates an array for the round robin algorithm
 */
function round_robin_array($array)
{
    // we always keep index 0
    $top = array_shift($array);
    $last = array_pop($array);
    $rotate = [$last];
    foreach ($array as $_value) {
        $rotate[] = $_value;
    }
    array_unshift($rotate, $top);
    return $rotate;
}

/**
 * Runs a round robin to make a schedule.
 */
function round_robin($players, $weeks)
{
    $schedule = [];
    $count = count($players);
    foreach ($players as $_p) {
        $schedule[$_p] = array_fill(0, $weeks, []);
    }
    for ($i=0;$i<$weeks;$i++) {
        for ($a=0;$a<($count / 2) + 1;$a++) {
            $vs = $players[$a];
            $opp = $players[($count - $a) - 1];
            $at = rand(0,1);
            $pg = [$opp, $at];
            $og = [$vs, $at];
            $schedule[$vs][$i] = $pg;
            $schedule[$opp][$i] = $og;
        }
        $players = round_robin_array($players);
    }
    return $schedule;
}