백준 스택 - 10828번 : 스택

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

10828번: 스택

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import java.util.*;
import java.io.*;

public 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));
		int a = Integer.parseInt(br.readLine());
		stack temp = new stack();
		StringTokenizer st;
		StringBuilder sb = new StringBuilder("");
		for(int i=0; i<a; i++) {
			st = new StringTokenizer(br.readLine());
			String command =st.nextToken();
			if(command.equals("push")) {
				int num = Integer.parseInt(st.nextToken());
				temp.push(num);
			}
			else if(command.equals("pop")){
				sb.append(temp.pop()+"\n");
			}
			else if(command.equals("size")) {
				sb.append(temp.size()+"\n");
			}
			else if(command.equals("empty")) {
				sb.append(temp.empty()+"\n");
			}
			else {
				sb.append(temp.top()+"\n");
			}
			
		}
		
		bw.write(sb+"");
		bw.close();
	}
	
}
class stack{
	int top = -1;
	private int size = 0;
	ArrayList<Integer> al = new ArrayList<>();
	void push(int num) {
		al.add(0,num);
		size++;
	}
	int pop() {
		if(size==0) return -1;
		size--;
		return al.remove(0);
	}
	int size() {
		return size;
	}
	int empty() {
		if(size==0) return 1;
		else return 0;
	}
	int top() {
		if(size==0) return top;
		return al.get(0);
	}
}