문제 난이도 : Easy

문제 유형 : Data Structures - Queues

문제 설명 간략 :

두개의 stack을 이용하여 Queue(FIFO)를 구현하라.

1 x: Enqueue element into the end of the queue.

2: Dequeue the element at the front of the queue.

3: Print the element at the front of the queue.

제약사항

• 1 <= q <= 10^5
• 1 <= type <= 3

• 1 <=

  x

  <= 10^9

자바 풀이

import java.io.*;
import java.util.*;

public class Solution {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int quries = in.nextInt();

        Stack<Integer> one = new Stack<Integer>();
        Stack<Integer> two = new Stack<Integer>();

        int query;

        for(int i = 0; i < quries; i++) {
            query = in.nextInt();

            if(query == 1) {
                one.push(in.nextInt());
            }else if(query == 2) {
                if(two.isEmpty()){
                    while(!one.isEmpty()) {
                        two.push(one.pop());
                    }
                }

                if(!two.isEmpty()){
                    two.pop();
                }
            }else if(query == 3) {
                if(two.isEmpty()) {
                    while(!one.isEmpty()) {
                        two.push(one.pop());
                    }
                    System.out.println(two.peek());
                }else {
                    System.out.println(two.peek());
                }
            }
        }
    }
}

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