Priority Queue

https://www.acmicpc.net/problem/1927

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.PriorityQueue;

public class Main {
    public static void main(String[] args) throws Exception {
        int N, X;
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        N = Integer.parseInt(br.readLine());
        PriorityQueue pq = new PriorityQueue<Integer>();
        for(int i=0; i<N; i++){
            X = Integer.parseInt(br.readLine());
            if(X==0){
                if(pq.peek() == null){
                    System.out.println(0);
                }
                else{
                    System.out.println(pq.poll());
                }
            }
            else{
                pq.add(X);
            }
        }
    }

}