백준 JAVA 10845 큐

https://www.acmicpc.net/problem/10845

10845번: 큐

 

package BAEKJOON.Silver.Ⅳ;

import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;

public class NO10845 {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        StringBuilder sb = new StringBuilder();
        Queue<Integer> Q = new LinkedList<>();
        int n = sc.nextInt();
        int num = 0;

        for (int i = 0; i < n; i++) {
            String str = sc.next();
            if (str.equals("push")) {
                num = sc.nextInt();
                Q.add(num);
            } else if (str.equals("pop")) {
                if (Q.isEmpty()) {
                    sb.append(-1).append("\n");
                } else {
                    sb.append(Q.poll()).append("\n");
                }
            } else if (str.equals("size")) {
                sb.append(Q.size()).append("\n");
            } else if (str.equals("front")) {
                if (Q.isEmpty()) {
                    sb.append(-1).append("\n");
                } else {
                    sb.append(Q.peek()).append("\n");
                }
            } else if (str.equals("empty")) {
                if (Q.isEmpty()) {
                    sb.append(1).append("\n");
                } else {
                    sb.append(0).append("\n");
                }
            } else if (str.equals("back")) {
                if (Q.isEmpty()) {
                    sb.append(-1).append("\n");
                } else {
                    sb.append(num).append("\n");
                }
            }
        }
        System.out.println(sb);
    }
}