题解 | #判断两个IP是否属于同一子网#

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 in = new Scanner(System.in);

        while (in.hasNext()) {

            for (int i = 0; i < 3; i++) {
                String yM = in.nextLine();
                String ip1 = in.nextLine();
                String ip2 = in.nextLine();


                String[] yMArr = yM.split("\\.");
                String[] ip1Arr = ip1.split("\\.");
                String[] ip2Arr = ip2.split("\\.");

                boolean b = true;

                
                for(int n = 0; n < yMArr.length; n++){
                    String numStr = yMArr[n];
                    int ymSeInt = Integer.valueOf(numStr);
                    if(ymSeInt < 0){
                        b = false;
                    }
                    if(ymSeInt > 255){
                        b = false;
                    }

                }

                int yMInt = getIpInt(yMArr);
                String yMTemp =  Integer.toBinaryString(yMInt);

                while(yMTemp.length() < 32){
                    yMTemp = 0 + yMTemp;
                }

                //yMTemp = String.format("%032d", yMTemp);
                int bJ = -1;
                for (int k = 0; k < yMTemp.length(); k++) {
                    if (k + 1 >= yMTemp.length() - 1) {
                        break;
                    }
                    if (yMTemp.charAt(k) != yMTemp.charAt(k + 1)) {
                        bJ = k + 1;
                        break;
                    }
                }

                if (bJ != -1) {
                    String s1 = yMTemp.substring(bJ);
                    if (s1.contains("1")) {
                        // 非法
                        b = false;
                    }
                }


                if (!b || !checkIp(ip1Arr) || !checkIp(ip2Arr)) {
                    // 非法
                    System.out.println(1);
                    break;
                }


                int ip1Int = getIpInt(ip1Arr);
                int ip2Int = getIpInt(ip2Arr);

                if ((ip1Int & yMInt) == (ip2Int & yMInt)) {
                    System.out.println(0);
                    break;
                } else {
                    System.out.println(2);
                    break;
                }

            }
        }
    }

    private static boolean checkIp(String[] ipArr) {
        for (int i = 0; i < ipArr.length; i++) {
            String temp = ipArr[i];
            int ip1Int = Integer.valueOf(temp);
            if (ip1Int < 0 || ip1Int >= 255) {
                return false;
            }
        }
        return true;
    }

    private static int getIpInt(String[] ipArr) {

        int resInt = 0;
        for (int i = 0; i < ipArr.length; i++) {
            String temp = ipArr[i];
            int ip1Int = Integer.valueOf(temp);
            resInt += ip1Int << 8 * (3 - i);
        }

        return resInt;
    }

}