PHP에서의 분리된 집합(Union-Find 알고리즘)

class DisjointSet
{
    private $parent = [];
    private $rank   = [];

    public function __construct($size)
    {
        for ($i = 0; $i < $size; $i++)
        {
            $this->parent[$i]   = $i;
            $this->rank[$i]     = 0;
        }
    }

    public function find($x)
    {
        if ($this->parent[$x] != $x)
        {
            $this->parent[$x] = $this->find($this->parent[$x]);
        }

        return $this->parent[$x];
    }

    public function union($x, $y)
    {
        $rootX = $this->find($x);
        $rootY = $this->find($y);

        if ($rootX != $rootY)
        {
            if ($this->rank[$rootX] > $this->rank[$rootY])
            {
                $this->parent[$rootY] = $rootX;
            }
            elseif ($this->rank[$rootX] < $this->rank[$rootY])
            {
                $this->parent[$rootX] = $rootY;
    
            }
            else
            {
                $this->parent[$rootY] = $rootX;
                $this->rank[$rootX]++;
            }
        }
    }
}