stack_2.由两个栈组成队列

思路：

用两个栈（$stack_a, $stack_b），当push的时候，压入$stack_a, 让pop的时候，先把$stack_a元素依次全部倒入$stack_b中，再对$stack_b进行pop，然后再还原$stack_a,$stack_b(把$stack_b倒入stack_a)

<?php

class StackQueue

{

    public $stack_a;

    public $stack_b;

    public function __construct()

    {

        $this->stack_a = new SplStack();

        $this->stack_b = new SplStack();

    }

    public function pop()

    {

        $this->exchange($this->stack_a, $this->stack_b);

        $pop = $this->stack_b->pop();

        $this->exchange($this->stack_b, $this->stack_a);

        return $pop;

    }

    public function push($value)

    {

        $push = $this->stack_a->push($value);

        return $push;

    }

    public function exchange($stack_a, $stack_b)

    {

        $count = $stack_a->count();

        for ($i = 0; $i < $count; $i++) {

            $pop = $stack_a->pop();

            $stack_b->push($pop);

        }

    }

}

$StackQueue = new StackQueue();

$StackQueue->push(1);

$StackQueue->push(2);

echo $StackQueue->pop();

echo $StackQueue->pop();

巴特西

stack_2.由两个栈组成队列

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