题解 | #识别有效的IP地址和掩码并进行分类统计#

import java.util.Arrays;
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int aCount = 0, bCount = 0, cCount = 0, dCount = 0, eCount = 0, errorCount = 0, privateCount = 0;
        while (scanner.hasNextLine()) {
            String s = scanner.nextLine();
            try {
                String[] arr = s.split("~");
                int[] ipArr = Arrays.asList(arr[0].split("\\.")).stream().mapToInt(Integer::valueOf).toArray();
                int[] maskArr = Arrays.asList(arr[1].split("\\.")).stream().mapToInt(Integer::valueOf).toArray();
                if (ipArr.length != 4 || maskArr.length != 4) {
                    throw new Exception();
                }
                for (int i = 0; i < 4; i++) {
                    if (ipArr[i] < 0 || ipArr[i] > 255 || maskArr[i] < 0 || maskArr[i] > 255) {
                        throw new Exception();
                    }
                }
                if (ipArr[0] != 0 && ipArr[0] != 127) {// 检查子网掩码
                    String bi = "";
                    for (int i = 0; i < 4; i++) {
                        String b = Integer.toBinaryString(maskArr[i]);
                        while (b.length() != 8) {
                            b = "0" + b;
                        }
                        bi += b;
                    }
                    if (bi.charAt(0) != 49 || bi.charAt(bi.length() - 1) != 48) {
                        throw new Exception();
                    }
                    int left = 0, right = bi.length() - 1;
                    for (;left < right; left++) {
                        if (bi.charAt(left) == 48) {
                            break;
                        }
                    }
                    for (;right >= 0; right--) {
                        if (bi.charAt(right) == 49) {
                            break;
                        }
                    }
                    if (left - right != 1) {
                        throw new Exception();// 非法子网掩码
                    }
                }
                if (ipArr[0] >= 240 && ipArr[0] <= 255) {// e类地址
                    eCount++;
                } else if (ipArr[0] >= 224) {// d类地址
                    dCount++;
                } else if (ipArr[0] >= 192) {// c类地址
                    cCount++;
                } else if (ipArr[0] >= 128) {// b类地址
                    bCount++;
                } else if (ipArr[0] >= 1 && ipArr[0] <= 126) {// a类地址
                    aCount++;
                }
                if (ipArr[0] == 10 
                    || (ipArr[0] == 172 && ipArr[1] >= 16 && ipArr[1] <= 31) 
                    || (ipArr[0] == 192 && ipArr[1] == 168)) {// 私有地址
                        privateCount++;
                    }
            } catch (Exception e) {
                errorCount++;// 非法ip或非法子网掩码
            }
        }
        System.out.println(aCount + " " + bCount + " " + cCount + " " + dCount + " " 
                           + eCount + " " + errorCount + " " + privateCount);
    }
}