Tic Tac Toe Attempt 1 h 5 minutes

ttt.php

<?php

class TicTacToe
{
    const VALUE_X = "x";
    const VALUE_O = "o";

    protected $size;
    protected $board;
    protected $winner;

    public function __construct($size)
    {
        $this->size = $size;

        for ($i = 0; $i < $this->size; $i++) {
            $this->board[$i] = array_fill(0, $this->size, null);
        }
    }

    protected function checkColumn($i)
    {
        $value = $this->board[$i][0];

        if (!is_null($value)) {
            for ($j = 1; $j < $this->size; $j++) {
                if ($value !== $this->board[$i][$j]) {
                    return null;
                }
            }
        }

        return $value;
    }

    protected function checkRow($j)
    {
        $value = $this->board[0][$j];

        if (!is_null($value)) {
            for ($i = 1; $i < $this->size; $i++) {
                if ($value !== $this->board[$i][$j]) {
                    return null;
                }
            }
        }

        return $value;
    }

    protected function checkDiagonal()
    {
        $value = $this->board[0][0];

        if (!is_null($value)) {
            for ($i = 1; $i < $this->size; $i++) {
                if ($value !== $this->board[$i][$i]) {
                    return null;
                }
            }
        }

        return $value;
    }

    protected function checkBackDiagonal()
    {
        $value = $this->board[$this->size - 1][0];

        if (!is_null($value)) {
            for ($i = $this->size - 1; $i <= 0; $i--) {
                if ($value !== $this->board[$i][$this->size - $i]) {
                    return null;
                }
            }
        }

        return $value;
    }

    public function check()
    {
        // columns
        for ($i = 0; $i < $this->size; $i++) {
            if ($value = $this->checkColumn($i)) {
                return $value;
            }
        }

        // rows
        for ($j = 0; $j < $this->size; $j++) {
            if ($value = $this->checkRow($j)) {
                return $value;
            }
        }

        // diagonals
        if ($value = $this->checkDiagonal()) {
            return $value;
        }

        if ($value = $this->checkBackDiagonal()) {
            return $value;
        }

        return null;
    }

    protected function won($value)
    {
        $this->winner = $value;
        print "Winner is {$this->winner} \n";
    }

    public function play($i, $j, $value)
    {
        if ($this->winner) {
            print "{$this->winner} already won \n";
            return;
        }

        $this->board[$i][$j] = $value;
        $this->printBoard();

        $value = $this->check();

        if (!is_null($value)) {
            $this->won($value);
        }
    }

    protected function printBoard()
    {
        for ($j = 0; $j < $this->size; $j++) {
            // print("--- \n");
            for ($i = 0; $i < $this->size; $i++) {
                $value = $this->board[$i][$j] ?? " ";
                print(" $value |");
            }
            print("\n");
        }

        print(" ------------ \n");
    }
}

$game = new TicTacToe(3);
$game->play(0, 0, TicTacToe::VALUE_O);
$game->play(0, 1, TicTacToe::VALUE_X);
$game->play(1, 0, TicTacToe::VALUE_O);
$game->play(1, 1, TicTacToe::VALUE_X);
$game->play(2, 0, TicTacToe::VALUE_O);