[백준] 10845번 : 큐 - Java(자바)

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

import java.util.*;
class Queue {
    int first;
    int last;
    int[] queue;
    
    public Queue(int num){
        queue = new int[num];
        first=0;
        last=0;
    }
    public void push(int num) {
        queue[last] = num;
		last++;
    }
    public int pop() {
		if(last-first == 0) return -1;
		else {
			int ans = queue[first];
			queue[first] = 0;
			first++;
			return ans;
		}
	}
	public int size() {
		return last-first;
	}
	public int empty() {
		if(last-first == 0) return 1;
		else return 0;
	}
	public int front() {
		if(last-first == 0) return -1;
		else return queue[first];
	}
	public int back() {
		if(last-first == 0) return -1;
		else return queue[last - 1];
	}
}
public class Main {
    public static void main(String args[]) {
        Scanner s=new Scanner(System.in);
        StringBuilder sb = new StringBuilder();
        int n=s.nextInt();
        Queue t=new Queue(n);
        
        for(int i=0;i<n;i++) {
			String st = s.next();
			switch (st) {
			case "push":
				t.push(s.nextInt());
				break;
			case "pop":
				sb.append(t.pop()).append('\n');
				break;
			case "size":
				sb.append(t.size()).append('\n');
				break;
			case "empty":
				sb.append(t.empty()).append('\n');
				break;
			case "front":
				sb.append(t.front()).append('\n');
				break;
			case "back":
				sb.append(t.back()).append('\n');
				break;
			}
		}
		System.out.println(sb);
    }
}