题解 | 【模板】栈

import java.util.*;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        int n = in.nextInt();
        String line;
        in.nextLine();
        MyStack myStack = new MyStack();
        for (int l = 0; l < n; l++) {
            line = in.nextLine();
            String[] opt = line.split(" ");
            if (opt[0].equals("push")) {
                myStack.push(Integer.valueOf(opt[1]));
            } else if (opt[0].equals("pop")) {
                try {
                    System.out.println(myStack.pop());
                } catch (Exception e) {
                    System.out.println("error");
                }
            } else if (opt[0].equals("top")) {
                try {
                    System.out.println(myStack.peek());
                } catch (Exception e) {
                    System.out.println("error");
                }
            }
        }
    }
}

class MyStack {
    LinkedList<Integer> list;
    public MyStack() {
        this.list = new LinkedList<>();
    }

    public void push(int num) {
        list.add(num);
    }

    public int peek() {
        return list.get(list.size() - 1);
    }

    public int pop() {
        int res = list.get(list.size() - 1);
        list.remove(list.size() - 1);
        return res;
    }
}