[백준 10828] 스택

문제

https://www.acmicpc.net/problem/10828

10828번: 스택

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내가 작성한 코드

import java.io.*;
import java.util.Stack;
import java.util.StringTokenizer;

public class qor10828 {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));

        int num = Integer.parseInt(br.readLine());
        Stack<Integer> number = new Stack<>();

        for(int i = 0; i<num; i++){
            StringTokenizer st = new StringTokenizer(br.readLine());

            String word = st.nextToken();

            if(word.equals("push")){
                int addnum = Integer.parseInt(st.nextToken());

                number.add(addnum);
            }
            else if(word.equals("pop")){
                if(number.isEmpty()){
                    bw.write("-1"+"\n");
                }
                else{
                    bw.write(number.pop()+"\n");
                }
            }
            else if(word.equals("size")){
                bw.write(number.size()+"\n");
            }
            else if(word.equals("empty")){
                if(number.isEmpty()){
                    bw.write("1"+"\n");
                }
                else{
                    bw.write("0"+"\n");
                }
            }
            else{
                if(number.isEmpty()){
                    bw.write("-1"+"\n");
                }
                else{
                    bw.write(number.get(number.size()-1)+"\n");
                }
            }
        }

        bw.close();
    }
}