RoundRobin.php

<?php

namespace lloc\tournament;

/**
 * Class RoundRobin
 *
 * @package lloc\tournament
 */
class RoundRobin {

	/**
	 * @var int
	 */
	protected $players;

	/**
	 * RoundRobin constructor.
	 *
	 * @param int $players
	 */
	public function __construct( int $players ) {
		$this->players = $players % 2 == 0 ? $players : $players + 1;
	}

	/**
	 * Gets round robin table
	 *
	 * @return array
	 */
	function get() {
		$result = [];

		for ( $rounds = 0; $rounds < $this->players - 1; $rounds++ ) {
			for ( $i = 0; $i < $this->players / 2; $i++ ) {
				$result[ $rounds ][] = [
					( $i == 0 ? 0 : ( $rounds + $i ) % ( $this->players - 1 ) + 1 ),
					( $this->players - 1 + $rounds - $i ) % ( $this->players - 1 ) + 1,
				];
			}
		}

		return $result;
	}

}