PHP Stack Implementation

data-structures, php, stack

Solution

Change your constructor as follows:

<?php

class Stack {

    protected $stack;
    protected $limit;

    public function __construct($limit = 10, $initial = array()) {
        // initialize the stack
        $this->stack = $initial;
        // stack can only contain this many items
        $this->limit = $limit;
    }

    public function push($item) {
        // trap for stack overflow
        if (count($this->stack) < $this->limit) {
            // prepend item to the start of the array
            array_unshift($this->stack, $item);
        } else {
            throw new RunTimeException('Stack is full!');
        }
    }

    public function pop() {
        if ($this->isEmpty()) {
            // trap for stack underflow
            throw new RunTimeException('Stack is empty!');
        } else {
            // pop item from the start of the array
            return array_shift($this->stack);
        }
    }

    public function top() {
        return current($this->stack);
    }

    public function isEmpty() {
        return empty($this->stack);
    }

}

/**
 * This'll work as expected.
 */
$stack = new Stack();
$stack->push(1);
$stack->push(2);
$stack->push(3);
$stack->push(4);
$stack->push(5);

/**
 * And this too.
 */
$stack = new Stack(10, array(1, 2, 3, 4, 5));

Just FYI, PHP has `array_push` (http://php.net/manual/en/function.array-push.php) and `array_pop` (https://www.php.net/array_pop) implementations.

Problem

Original source