Data commit

Task/Canonicalize-CIDR/C-sharp/canonicalize-cidr.cs

@@ -0,0 +1,63 @@
+using System;
+using System.Net;
+using System.Linq;
+
+public class Program
+{
+    public static void Main()
+    {
+        string[] tests = {
+            "87.70.141.1/22",
+            "36.18.154.103/12",
+            "62.62.197.11/29",
+            "67.137.119.181/4",
+            "161.214.74.21/24",
+            "184.232.176.184/18"
+        };
+
+        foreach (string t in tests) Console.WriteLine($"{t}   =>   {Canonicalize(t)}");
+    }
+
+    static string Canonicalize(string cidr) => CIDR.Parse(cidr).Canonicalize().ToString();
+}
+
+readonly struct CIDR
+{
+    public readonly IPAddress ip;
+    public readonly int length;
+
+    public static CIDR Parse(string cidr)
+    {
+        string[] parts = cidr.Split('/');
+        return new CIDR(IPAddress.Parse(parts[0]), int.Parse(parts[1]));
+    }
+
+    public CIDR(IPAddress ip, int length) => (this.ip, this.length) = (ip, length);
+
+    public CIDR Canonicalize() =>
+        new CIDR(
+            new IPAddress(
+                ToBytes(
+                    ToInt(
+                        ip.GetAddressBytes()
+                    )
+                    & ~((1 << (32 - length)) - 1)
+                )
+            ),
+            length
+        );
+
+    private int ToInt(byte[] bytes) => bytes.Aggregate(0, (n, b) => (n << 8) | b);
+
+    private byte[] ToBytes(int n)
+    {
+        byte[] bytes = new byte[4];
+        for (int i = 3; i >= 0; i--) {
+            bytes[i] = (byte)(n & 0xFF);
+            n >>= 8;
+        }
+        return bytes;
+    }
+
+    public override string ToString() => $"{ip}/{length}";
+}