题解 | #整数与IP地址间的转换#

import java.util.*;

// 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 ip = in.nextLine();
           
            if (ip.contains(".")) {
    
                String[] ipnum = ip.split("\\.");
                long res = 0;
                for (int i = 0; i < ipnum.length; i++) {
                    int tempNum = Integer.parseInt(ipnum[i]);
                    res += tempNum * Math.pow(2, (ipnum.length - i - 1) * 8);
                }
                System.out.println(res);

            } else {
   
                int[] resNum = new int[4];
                long aimNum = Long.parseLong(ip);
                for (int i = 0; i < 4; i++) {
                    resNum[i] = (int) (aimNum / Math.pow(2, 8 * (3 - i)));
                    aimNum =  (long) (aimNum % Math.pow(2, 8 * (3 - i)));
                }
                String resStr = "";
                for (int i = 0; i < 4; i++) {
                    resStr += resNum[i];
                    if (i != 3) {
                        resStr += ".";
                    }
                }

                System.out.println(resStr);
        
            }

        }
    }
}