题解 | #判断两个IP是否属于同一子网#

import java.util.Scanner;

// 都挤在一块哈哈
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNextLine()) {
            String mask = in.nextLine();
            String ip1 = in.nextLine();
            String ip2 = in.nextLine();
            String[] maskArr = mask.split("\\.");
            String[] ip1Arr = ip1.split("\\.");
            String[] ip2Arr = ip2.split("\\.");
            if (maskArr.length != 4 || ip1Arr.length != 4 || ip2Arr.length != 4) {
                System.out.println(1);
                continue;
            }
            StringBuilder sb = new StringBuilder();
            int temp = 0;
            for (int j = 0; j < 4; j++) {
                if (Integer.parseInt(ip1Arr[j]) > 255 || Integer.parseInt(ip1Arr[j]) < 0 ||
                        Integer.parseInt(ip2Arr[j]) > 255 || Integer.parseInt(ip2Arr[j]) < 0 ||
                        Integer.parseInt(maskArr[j]) > 255 || Integer.parseInt(maskArr[j]) < 0) {
                    System.out.println(1);
                    temp = 1;
                    break;
                }
                String binary = Integer.toBinaryString(Integer.parseInt(maskArr[j]));
                //不足8位补齐
                binary = String.format("%08d", Integer.parseInt(binary));
                sb.append(binary);
            }
            if (temp != 0) {
                continue;
            }
            if (sb.lastIndexOf("1") > sb.indexOf("0")) {
                System.out.println(1);
                continue;
            }

            for (int x = 0; x < 4; x++) {
                if ((Integer.parseInt(ip1Arr[x]) & Integer.parseInt(maskArr[x])) !=
                        (Integer.parseInt(ip2Arr[x]) & Integer.parseInt(maskArr[x]))) {
                    System.out.println(2);
                    temp = 1;
                    break;
                }
            }
            if (temp != 0) {
                continue;
            }
            System.out.println(0);
        }
    }
}