题解 | #整数与IP地址间的转换#

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextLine()) { // 注意 while 处理多个 case
            String str = in.nextLine();
            if (str.contains(".")) {
                pointToTen(str);
            } else {
                tenToPoint(str);
            }
        }
    }
    public static void pointToTen(String str) {
        String[] strArr = str.split("\\.");
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < strArr.length; i++) {
            String curStr = "00000000";
            String tempStr = Long.toString(Long.valueOf(strArr[i]), 2);
            curStr = (curStr + tempStr).substring(tempStr.length(), tempStr.length() + 8);
            sb.append(curStr);
        }
        System.out.println(Long.valueOf(sb.toString(), 2));
        return;
    }
    public static void tenToPoint(String str) {
        String[] strArr = new String[4];
        String bin = Long.toString(Long.valueOf(str), 2);
        int j = bin.length();
        for(int i=3;i>=0;i--) {
            strArr[i] = Long.valueOf(bin.substring(Math.max(0, j-8),j), 2).toString() ;
            j-=8;
        };
        System.out.println(String.join(".", strArr)); 
    }
}