题解 | #整数与IP地址间的转换#

32位二进制字符串补0有什么好方法吗

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 ip = in.nextLine();
            if (ip.contains(".")) {
                StringBuilder sb = new StringBuilder();
                for (String s : ip.split("\\.")) {
                    sb.append(String.format("%08d", Integer.valueOf(Integer.toBinaryString(Integer.parseInt(s)))));
                }
                System.out.println(Long.parseLong(sb.toString(), 2));
            } else {
                StringBuilder sb = new StringBuilder(Long.toBinaryString(Long.parseLong(ip)));
                while (sb.length() < 32) {
                    sb.insert(0, "0");
                }
                String[] ans = new String[4];
                for (int i = 0; i < 4; i++) {
                    ans[i] = String.valueOf(Integer.parseInt(sb.substring(i * 8, (i + 1) * 8), 2));
                }
                System.out.println(String.join(".", ans));
            }
        }
    }
}