题解 | 【模板】栈的操作

//top为即将入栈的元素的索引，当top为0的时候栈为空。这样做的目的是方便计算栈的size，直接用top表示
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        STACK stack=new STACK();
        int N=in.nextInt();
        for(int i=0;i<N;i++){
            String str=in.next();
            switch(str){
                case "push":
                    int temp=in.nextInt();
                    stack.push(temp);
                    break;
                case "pop":
                    stack.pop();
                    break;
                case "query":
                    stack.query();
                    break;
                case "size":
                    stack.size();
                    break;
            }
        }
        in.close();
    }
}
class STACK{
    public static final int MAX_L=100000;
    int[] arr=new int[MAX_L];
    int top=0;
    public void push(int x){
        arr[top]=x;
        top++;
    }
    public void pop(){
        if(top!=0){
            top--;
        }else{
            System.out.println("Empty");
        }
    }
    public void query(){
        if(top!=0){
            System.out.println(arr[top-1]);
        }else{
            System.out.println("Empty");
        }
    }
    public void size(){
        System.out.println(top);
    } 
}