题解 | #判断两个IP是否属于同一子网#

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Scanner;

// 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 scanner = new Scanner(System.in);
        while (scanner.hasNext()){
            String sy = scanner.nextLine();
            String sp1 = scanner.nextLine();
            String sp2= scanner.nextLine();
            //验证掩码与IP每一段在 0 - 255 之间
            ArrayList<String> pd = new ArrayList<>();
            pd.add(sy);
            pd.add(sp1);
            pd.add(sp2);
            boolean b = yanzheng1(pd);
            if (b){
                String s="";
                String[] split = sy.split("\\.");
                for (int i = 0; i <split.length; i++) {
                    String rb = rb(split[i]);
                    s=s+rb;//子网掩码32位2进制显示
                }
                if (s.matches("[1]{1,}[0]{1,}")){
                    String reb = reb(sy, sp1);
                    String reb2 = reb(sy, sp2);
                    if(reb.equals(reb2)){
                        System.out.println("0");
                    }else {
                        System.out.println("2");
                    }
                }else {
                    System.out.println("1");//子网掩码不对
                }
            }else {
                System.out.println("1");//0-255范围不对
            }
        }
    }
    public static String rb(String s){//10进制转2进制，如果长度小于8则补位0
        Integer integer = Integer.valueOf(s);
        String string = Integer.toString(integer, 2);
        HashMap<Integer, Integer> hm = new HashMap<>();
        hm.put(0,string.length());
        if (string.length()<8){
            for (int i = 0; i <8-hm.get(0); i++) {
                string="0"+string;
            }
        }
        return string;
    }
    public static boolean match(String s){//验证0-255范围
        Integer it = Integer.valueOf(s);
        if(it<0||it>255){
            return false;
        }
        return  true;
    }
    public static boolean yanzheng1(ArrayList<String> aa){//验证全部的12个字段的0-255范围
        for (int i = 0; i < aa.size(); i++) {
            String s = aa.get(i);
            String[] split = s.split("\\.");
            if (split.length!=4){
                return false;
            }else {
                for (int j = 0; j <split.length; j++) {
                    boolean match = match(split[j]);
                    if(!match){
                        return false;
                    }
                }
            }
        }
        return true;
    }
    public static String reb(String s,String d){//传入ip返回2进制32位串
        String[] split = s.split("\\.");
        String[] split2 = d.split("\\.");
        String st="";
        for (int i = 0; i <split.length; i++) {
            String s1 = split[i];
            String s2 = split2[i];
            Integer it1 = Integer.valueOf(s1);
            Integer it2 = Integer.valueOf(s2);
            int i1 = it1 & it2;
            String s3 = String.valueOf(i1);
            st=st+s3+".";
        }
        return st;
    }
}