릿코드 232. Implement Queue using Stacks 코틀린

스택2개를 큐처럼쓰려면,한쪽으로는 데이터 push,한쪽으로는 데이터 추출만 하면됨
이건 스택1에서 스택2로 전부 넣고 뽑으면 처음 스택1을 넣은순서대로 나온다는걸 기반으로 함
즉 팝이나 픽을 할땐,스택1에서 스택2로 다몰아넣고,하나뽑고 다시 스택1로 다시 다몰아넣으면됨



정답

import java.util.Stack

class MyQueue() {
    val stack1=Stack<Int>()
    val stack2=Stack<Int>()


    fun push(x: Int) {
        stack1.push(x)
    }

    fun pop(): Int {
        while (!stack1.empty()){
            stack2.push(stack1.pop())
        }
        val res=stack2.pop()
        while (!stack2.empty()){
            stack1.push(stack2.pop())
        }
        return res
    }

    fun peek(): Int {
        while (!stack1.empty()){
            stack2.push(stack1.pop())
        }
        val res=stack2.peek()
        while (!stack2.empty()){
            stack1.push(stack2.pop())
        }
        return res
    }

    fun empty(): Boolean {
        return stack1.empty()
    }

}