题解 | #【模板】栈#

import java.util.*;

class ArrayStack {
    private int maxSize;
    private int[] stack;
    private int top = -1;

    public ArrayStack(int maxSize) {
        this.maxSize = maxSize;
        stack = new int[this.maxSize];
    }

    public boolean isFull() {
        return top == maxSize - 1;
    }

    public boolean isEmpty() {
        return top == -1;
    }

    public void push(int value) {
        if (isFull()) {
            System.out.println("error");
            return;
        }
        top++;
        stack[top] = value;
    }

    public void pop() {
        if (isEmpty()) {
            System.out.println("error");
        } else {
            int value = stack[top];
            top--;
            System.out.println(value);
        }
    }

    public void printTop() {
        if (isEmpty()) {
            System.out.println("error");
        }else{
            int value = stack[top];
            System.out.println(value);
        }
        
    }

}

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int n = Integer.parseInt(scan.nextLine());
        ArrayStack stack = new ArrayStack(n);

        while (scan.hasNextLine()) {
            String str = (String)scan.nextLine();
            String arr[] = str.split(" ");
            if (arr[0].equals("push")) {
                stack.push(Integer.parseInt(arr[1]));
            } else if (arr[0].equals("pop")) {
                stack.pop();
            } else {
                stack.printTop();
            }
        }
        scan.close();

    }
}