题目描述

参照：整数与IP地址间的转换__牛客网

IP地址转整数

法一

注：Java中需要Long型，int会溢出

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import java.util.Scanner;

public class ipInt {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String strIp = sc.nextLine();
        String[] ipArr = strIp.split("\\.");

        Long n = Long.parseLong(ipArr[0]);

        for (int i = 1; i < 4; i++) {
            n = n << 8;  // 位运算将每一位往左移8
            n += Long.parseLong(ipArr[i]);
        }

        System.out.println(n);
    }
}

法二

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import java.util.Scanner;

public class ipInt {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String strIp = sc.nextLine();
        String[] ipArr = strIp.split("\\.");

        Long[] arr = new Long[4];
        for (int i = 0; i < 4; i++) {
            arr[i] = Long.parseLong(ipArr[i]);
        }

        Long res = 0L;
        res += arr[0] << 24;
        res += arr[1] << 16;
        res += arr[2] << 8;
        res += arr[3];
    //  上述运算等同于一句话：
    //  res = arr[0] << 24 | arr[1] << 16 | arr[2] << 8 | arr[3];
        
        System.out.println(res);
    }
}

法三

数字转32位2进制，最前面补0，然后分成4个8位2进制拼起来一个长字符串，再转10进制加上

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import java.util.Scanner;

public class ipInt {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String strIp = sc.nextLine();
        String[] ipArr = strIp.split("\\.");

        long[] ip = new long[4];
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < 4; i++) {
            ip[i] = Long.parseLong(ipArr[i]);
            String a = Long.toBinaryString(ip[i]);
            //转成8位二进制 利用String.format()控制格式
            String temp = String.format("%08d", Long.parseLong(a));
            sb.append(temp);
        }

        long output = Long.parseLong(sb.toString(), 2); // radix参数指定了二进制
        // valueOf()也行
        System.out.println(output);
    }
}

整数转IP地址

法一

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import java.util.Scanner;

public class intIp {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long strNum = Long.parseLong(sc.nextLine());

        String strIp = Long.toBinaryString(strNum);
        // 要在前面补足0
        StringBuilder sb = new StringBuilder();
        if (strIp.length() < 32) {
            for (int i = 0; i < (32 - strIp.length()); i++) {
                sb.append(0);
            }
            sb.append(strIp);
        } else if (strIp.length() == 32) {
            sb.append(strIp);
        }

        for (int i = 0; i < sb.length() - 8; i += 8) {
            System.out.print(Integer.parseInt(sb.substring(i, i + 8), 2) + ".");
        }

        System.out.println(Integer.parseInt(sb.substring(sb.length() - 8, sb.length()), 2));
    }
}

法二

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import java.util.Scanner;

public class intIp {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long strNum = Long.parseLong(sc.nextLine());

        String strIp = Long.toBinaryString(strNum);
        int len = strIp.length();
        StringBuilder sb = new StringBuilder(strIp);
        // 不足32位的前面补0
        for (int i = 0; i < 32 - len; i++) {
            sb.insert(0, "0");
        }
        String fin = sb.toString();
        long a = Long.valueOf(fin.substring(0, 8), 2);
        long b = Long.valueOf(fin.substring(8, 16), 2);
        long c = Long.valueOf(fin.substring(16, 24), 2);
        long d = Long.valueOf(fin.substring(24, 32), 2);
        System.out.println(a + "." + b + "." + c + "." + d);
    }
}

法三

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import java.util.Scanner;

public class intIp {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long d = Long.parseLong(sc.nextLine());

        String out = String.format("%d.%d.%d.%d", (d >> 24) & 0xff, (d >> 16) & 0xff, (d >> 8) & 0xff, d & 0xff);
        System.out.println(out);
    }
}