亲们，请帮我看看第一题哪错了？

public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);

        String nn=sc.nextLine();
        if(nn==null||nn.length()==0){
            System.out.println(0);
        }
        int n=new Integer(nn);
        if(n==0||n<4||n%2!=0)
            System.out.println(0);

        String str=sc.nextLine();
        String[] strings=str.split(" ");
        int[] arr=new int[strings.length];
        for(int i=0;i<strings.length;i++){
            arr[i]=new Integer(strings[i]);
        }
        Arrays.sort(arr);
        int max=arr[0]+arr[n-1];
        int min=arr[n/2-1]+arr[n/2];
        System.out.println(max-min);
    }