BOJ 백준온라인져지 10845 큐 풀이

예제 입력 

15
push 1
push 2
front
back
size
empty
pop
pop
pop
size
empty
pop
push 3
empty
front

예제 출력 

1
2
2
0
1
2
-1
0
1
-1
0
3

	import java.util.*;
	import java.io.*;
	/**
	* https://www.acmicpc.net/problem/10845
	* BOJ 백준온라인져지 10845 큐 풀이
	*/
	class Main {
	public static void main(String[] args) throws IOException{
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
	Queue<Integer> queue = new LinkedList<>();
	int N = Integer.parseInt(br.readLine());
	while(N-- > 0){
	String str1[] = br.readLine().split(" ");
	String temp = str1[0];
	if(temp.equals("push")){
	int number = Integer.parseInt(str1[1]);
	queue.offer(number);
	}else if(temp.equals("pop")){
	if(!isEmpty(queue, bw)){
	bw.write(queue.poll() + "\n");
	}
	}else if(temp.equals("size")){
	bw.write(queue.size() + "\n");
	}else if(temp.equals("empty")){
	bw.write((queue.isEmpty() ? 1 : 0) + "\n");
	}else if(temp.equals("back")){
	if(!isEmpty(queue, bw)){
	Iterator<Integer> it = queue.iterator();
	int tempInteger = 0;
	while(it.hasNext()) tempInteger = it.next();
	bw.write(tempInteger + "\n");
	}
	}else if(temp.equals("front")){
	if(!isEmpty(queue, bw)){
	bw.write(queue.peek() + "\n");
	}
	}
	}
	bw.flush();
	}
	private static boolean isEmpty(Queue<Integer> queue, BufferedWriter bw) throws IOException{
	if(queue.isEmpty()){
	bw.write("-1\n");
	}
	return queue.isEmpty();
	}
	}

view raw BOJ_10845.java hosted with ❤ by GitHub

front는 맨 처음에 offer된 변수를 출력하면 된다.

Java에서는 front같은 메소드가 없는거 같아서 iterator에서를

돌려서 출력해줬다.