PHP Data Structure: Stack

data-structure-stack.php

class Stack {
    protected $top;

    public function push($data) {
        $node = new Node($data);
        $node->next = $this->top;

        $this->top = $node;
    }

    public function pop() {
        $node = $this->top;
        $this->top = $this->top->next;

        return $node;
    }

    public function peek() {
        return $this->top->data;
    }
}

class Node {
    public $data;
    public $next;

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