PHP实现栈数据结构

<?php

class Stack{
const MAXSIZE = 4;// 栈最大容量
private $top = -1;
private $stack = array();// 利用数组存储数据

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

// 入栈
public function push($ele){
if ($this->top >= self::MAXSIZE-1){
echo 'stack is full...';
return false;
}
$this->stack[++$this->top] = $ele;// 此处必须是++i，先计算再使用
}

// 出栈，返回出栈元素
public function pop(){
if ($this->top == -1){
echo 'stack is empty...';
return false;
}
$ele = $this->stack[$this->top];
unset($this->stack[$this->top--]);// 此处必须是i--，先使用再计算（注意出栈和入栈的区别）
return $ele;
}

// 遍历栈
public function show(){
if ($this->top == -1){
echo 'stack is empty...';
return false;
}
for($i=$this->top; $i>-1; $i--){
echo $this->stack[$i].'<br/>';
}
}

}

$stack = new Stack;
$stack->push(1);
$stack->push(2);
$stack->push(3);
$stack->push(4);

//print_r($stack);
$stack->show();

$a = $stack->pop();
$a = $stack->pop();
$a = $stack->pop();

$stack->show();