题解 | #整数与IP地址间的转换#

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // ip转长整数
        String ip = in.nextLine();
        String[] split = ip.split("\\.");
        long result = 0L;
        result += Long.parseLong(split[0]) << 24;
        result += Long.parseLong(split[1]) << 16;
        result += Long.parseLong(split[2]) << 8;
        result += Long.parseLong(split[3]);
        System.out.println(result);
        // 长整数转ip
        String longStr = in.nextLine();
        long inputLong = Long.parseLong(longStr);
        StringBuilder binaryString = new StringBuilder(Long.toBinaryString(inputLong));
        while (binaryString.length() < 32) {
            // 不够32位前面补0直到补够32位（关键就在这里-Long.toBinaryString()方法计算出的二进制以1开头，0开头会省略）
            binaryString.insert(0, "0");
        }
        // 将二进制字符串转化成整数
        int a = Integer.parseInt(binaryString.substring(0, 8), 2);
        int b = Integer.parseInt(binaryString.substring(8, 16), 2);
        int c = Integer.parseInt(binaryString.substring(16, 24), 2);
        int d = Integer.parseInt(binaryString.substring(24), 2);
        System.out.println(a + "." + b + "." + c + "." + d);

    }
}