【牛客網】整數與IP地址間的轉換

網址鏈接

第一版答案：

package May16;

import java.util.*;

public class Demo12 {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNext()) {
            String ip = in.next();
            String address = in.next();
            System.out.println(ipToAddress(ip));
            System.out.println(addressToIp(address));

        }
    }

    public static String addressToIp(String address) {
        Integer integer = Integer.valueOf(address);
        String str = Integer.toBinaryString(integer);// 轉換成了二進制形式00000100101010
        int zero = 32 - str.length();
        for (int i = 0; i < zero; i++) {
            str = '0' + str;
        }

        String[] arr = new String[4];

        arr[0] = str.substring(0, 8);
        arr[1] = str.substring(8, 16);
        arr[2] = str.substring(16, 24);
        arr[3] = str.substring(24, 32);

        StringBuffer sb = new StringBuffer();

        for (int i = 0; i < 4; i++) {
            // 每個8位二進制要轉換成10進制
            int sum = 0;
            for (int j = 0; j < 8; j++) {
                if (arr[i].charAt(j) == '1') {
                    sum += (int) Math.pow(2, (7 - j));
                }
            }
            sb.append(sum);
            if (i != 3)
                sb.append(".");
        }
        return sb.toString();
    }

    public static int ipToAddress(String ip) {
        String[] arr = ip.split("\\.");
        int[] arrInt = new int[4];
        for (int i = 0; i < 4; i++) {
            arrInt[i] = Integer.valueOf(arr[i]);
        }
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < 4; i++) {
            String str = Integer.toBinaryString(arrInt[i]);// 轉換成了000001111形式
            int zero = 8 - str.length();
            for (int j = 0; j < zero; j++) {
                str = "0" + str;
            }
            sb.append(str);
        }
        // 合併了。0000100100010101010的形式
        String binary = sb.toString();
        int res = 0;
        int count = 0;
        for (int i = binary.length() - 1; i >= 0; i--) {
            if (binary.charAt(i) == '1')
                res += (int) Math.pow(2, count);
            count++;
        }
        return res;
    }


}

第二版答案：將第一版的int換成了long

爲什麼呢？int是4字節的。範圍爲-2³¹~2³¹-1。假設你的ip地址爲255.255.255.255 那麼需要將1111…1111一共32個1組成的二進制數轉成十進制。已經超出int的範圍了。所以要用long來代替int。

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNext()) {
            String ip = in.next();
            String address = in.next();
            System.out.println(ipToAddress(ip));
            System.out.println(addressToIp(address));

        }
    }

    public static String addressToIp(String address) {
        Long integer = Long.valueOf(address);
        String str = Long.toBinaryString(integer);// 轉換成了二進制形式00000100101010
        int zero = 32 - str.length();
        for (int i = 0; i < zero; i++) {
            str = '0' + str;
        }

        String[] arr = new String[4];

        arr[0] = str.substring(0, 8);
        arr[1] = str.substring(8, 16);
        arr[2] = str.substring(16, 24);
        arr[3] = str.substring(24, 32);

        StringBuffer sb = new StringBuffer();

        for (int i = 0; i < 4; i++) {
            // 每個8位二進制要轉換成10進制
            int sum = 0;
            for (int j = 0; j < 8; j++) {
                if (arr[i].charAt(j) == '1') {
                    sum += (int) Math.pow(2, (7 - j));
                }
            }
            sb.append(sum);
            if (i != 3)
                sb.append(".");
        }
        return sb.toString();
    }

    public static long ipToAddress(String ip) {
        String[] arr = ip.split("\\.");
        int[] arrInt = new int[4];
        for (int i = 0; i < 4; i++) {
            arrInt[i] = Integer.valueOf(arr[i]);
        }

        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < 4; i++) {
            String str = Integer.toBinaryString(arrInt[i]);// 轉換成了000001111形式
            int zero = 8 - str.length();
            for (int j = 0; j < zero; j++) {
                str = "0" + str;
            }
            sb.append(str);
        }
        // 合併了。0000100100010101010的形式
        String binary = sb.toString();


        long res = 0;
        int count = 0;
        for (int i = binary.length() - 1; i >= 0; i--) {
            if (binary.charAt(i) == '1')
                res += (long) Math.pow(2, count);
            count++;
        }
        return res;
    }


}