题解 | #【模板】栈#

import java.lang.; import java.util.; public class Main {

public static void main(String[] args){
    Scanner in = new Scanner(System.in);
    int size = in.nextInt();
    int index = 0;
    int[] arr = new int[size];
    int ops = 0;
    while(in.hasNext()) {
        String command = in.nextLine();
        if(command.startsWith("push")) {
            ops++;
            String[] commands = command.split(" ");
            arr[index++] = Integer.valueOf(commands[1]);
         }
        if(command.startsWith("pop")) {
            ops++;
            if(index==0) {
                System.out.println("error");
            } else 
            System.out.println(arr[--index]);            
        }
        if(command.startsWith("top")) {
            ops++;
            if(index==0) {
                System.out.println("error");
            }else
            System.out.println(arr[index-1]);
        }
        if(ops>=size){
            break;
        }
    }
}

}