algorithm - 在 Scala 中覆盖函数推送

Question

题目来自cracking-coding-interview，题目3.2

Stack Min: How would you design a stack which, in addition to push and pop, has a function min which returns the minimum element? Push, pop and min should all operate in 0(1) time.

然后我写了下面的代码，但是push函数是错误的，因为类型不兼容，不确定问题所在，为什么pop是正确的？谢谢

import scala.collection.mutable.Stack

class StackMin extends Stack[Int] {
  val minstack=new Stack[Int]

  override def push(element: Int): Stack[Int]={
    if (element<= min()){
      minstack.push(element)
    }
    super.push(element)
  }

  override def pop(): Int={
    val value=super.pop()
    if(value==min())
      minstack.pop()
    value
  }

  def min():Int={
    if(minstack.isEmpty)
      Int.MaxValue
    else minstack.top
  }
}

Answer 1

聪明的解决方案。

push 方法的返回类型错误。您可以将其指定为 StackMin.this.type:

override def push(element: Int): StackMin.this.type = {

或者完全忽略它(让编译器推断它):

override def push(element: Int) = {