题解 | #整数与IP地址间的转换#

using System;

class Program {
    public static void Main() {
        long chip = 0;
        long ip10 = 0;
        // 1 IP to decimal.
        var shift = 3;
        for(var ch=Console.Read(); ch!='\n'; ch=Console.Read()) {
            if (ch == '.') {
                ip10 |= chip << (shift*8);
                shift -= 1;
                chip = 0;
            } else {
                chip = chip*10 + ch-'0';
            }
        }
        ip10 |= chip;
        Console.WriteLine(ip10);
        // 2 Decimal to IP.
        ip10 = 0;
        for(var ch=Console.Read(); ch!='\n'; ch=Console.Read()) {
            ip10 = ip10*10 + ch-'0';
        }
        Console.Write((byte)(ip10 >> 24));
        Console.Write('.');
        Console.Write((byte)(ip10 >> 16));
        Console.Write('.');
        Console.Write((byte)(ip10 >> 8));
        Console.Write('.');
        Console.Write((byte)(ip10 >> 0));
    }
}