面试题 03.02. 栈的最小值
地址:https://leetcode-cn.com/problems/min-stack-lcci/
<?php /** * * 请设计一个栈,除了常规栈支持的pop与push函数以外,还支持min函数,该函数返回栈元素中的最小值。执行push、pop和min操作的时间复杂度必须为O(1)。 * * * 示例: * * MinStack minStack = new MinStack(); * minStack.push(-2); * minStack.push(0); * minStack.push(-3); * minStack.getMin(); --> 返回 -3. * minStack.pop(); * minStack.top(); --> 返回 0. * minStack.getMin(); --> 返回 -2. */ class MinStack { /** * initialize your data structure here. */ private $stack = null; private $order = null; function __construct() { $this->stack = []; $this->order = [PHP_INT_MAX]; } /** * @param Integer $x * @return NULL */ function push($x) { $this->stack[] = $x; //截止目前最小值入栈 if (end($this->order) > $x) { $this->order[] = $x; } else { $this->order[] = end($this->order); } } /** * @return NULL */ function pop() { $x = array_pop($this->stack); array_pop($this->order); return $x; } /** * @return Integer */ function top() { return end($this->stack); } /** * @return Integer */ function getMin() { return end($this->order); } } /** * Your MinStack object will be instantiated and called as such: * $obj = MinStack(); * $obj->push($x); * $obj->pop(); * $ret_3 = $obj->top(); * $ret_4 = $obj->getMin(); */ $obj = new MinStack(); $obj->push(-2); $obj->push(0); $obj->push(-3); $obj->pop(); $res_3 = $obj->top(); $ret_4 = $obj->getMin();