AcWing828.模拟栈

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import java.util.Scanner;

public class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int[] stl = new int[100010];//栈
        int m = sc.nextInt();//输入次数
        int tt = 0;//栈顶
        while (m-- > 0){
            String s = sc.next();
            if (s.equals("push")){
                int x = sc.nextInt();
                stl[++tt] = x;
            } else if (s.equals("pop")){
                tt--;
            } else if (s.equals("empty")){
                if (tt > 0){
                    System.out.println("NO");
                } else {
                    System.out.println("YES");
                }
            } else {
                System.out.println(stl[tt]);
            }
        }
    }
}