cidr4_merger.py

@@ -1,6 +1,8 @@
 from copy import deepcopy
 from ipaddress import IPv4Address
 from typing import List, Tuple
+from itertools import groupby
+from collections import defaultdict
 
 
 def get_data(input_file):
@@ -15,43 +17,45 @@ def cidr4_to_binary(cidr4: str) -> str:
     ipv4 = IPv4Address(ip_str)
     binary_ip = bin(int(ipv4))[2:]
     binary_ip = binary_ip.zfill(32)
-    binary = binary_ip[:vlsm]
+    binary = binary_ip[:vlsm] + "0" * (32 - vlsm)
     return binary
 
 
 def binary_to_cidr4(binary: str) -> str:
-    vlsm = len(binary)
-    binary_ip = binary + "0" * (32 - vlsm)
-    int_ip = int(binary_ip, 2)
+    vlsm = binary.rfind("1") + 1 if "1" in binary else 0
+    int_ip = int(binary, 2)
     ip = IPv4Address(int_ip)
     return f"{ip}/{vlsm}"
 
 
 def reduce_binary(binary: str) -> str:
-    if len(binary) == 0:
-        return ""
-    new_binary = binary[:-1]
-    if "1" not in new_binary:
-        return ""
-    return new_binary
+    assert len(binary) == 32
+    vlsm = binary.rfind("1")
+    if vlsm == -1:
+        return binary
+    return binary[:vlsm] + "0" + binary[vlsm + 1 :]
 
 
 def rough_merge_binaries(binaries: List[str], req_len: int) -> List[str]:
     ips = set(deepcopy(binaries))
     non_reducible_ips = set()
     reduction_limit_reached = False
+    max_vlsm = float("inf")
     while (
         len(ips) > 0
         and len(ips) + len(non_reducible_ips) > req_len
         and not reduction_limit_reached
+        and max_vlsm != -1
     ):
-        max_vlsm = len(max(ips, key=lambda x: len(x)))
+        ip_with_max_vlsm = max(ips, key=lambda x: x.rfind("1"))
+        max_vlsm = ip_with_max_vlsm.rfind("1")
+        print(f"{max_vlsm=}")
         reduced_ips = set()
         merged_ips = set()
         for ip in ips:
-            if len(ip) == max_vlsm:
+            if ip.rfind("1") == max_vlsm:
                 reduced_ip = reduce_binary(ip)
-                if len(reduced_ip) > 0:
+                if "1" in reduced_ip:
                     reduced_ips.add(reduced_ip)
                 else:
                     non_reducible_ips.add(ip)
@@ -62,6 +66,7 @@ def rough_merge_binaries(binaries: List[str], req_len: int) -> List[str]:
             ips = merged_ips
         else:
             reduction_limit_reached = True
+        print(f"{len(ips)=}")
 
     ips.update(non_reducible_ips)
     return sorted(ips)
@@ -73,6 +78,7 @@ def main():
 
     data = get_data(file)
     bin_ips = list(map(cidr4_to_binary, data))
+
     rough_merged_bin_ips = rough_merge_binaries(bin_ips, required_len)
     print(f"{len(rough_merged_bin_ips)=}")
     for ip in rough_merged_bin_ips:
@@ -80,19 +86,22 @@ def main():
 
 
 if __name__ == "__main__":
-    assert cidr4_to_binary("4.78.139.0/24") == "000001000100111010001011"
-    assert cidr4_to_binary("128.0.0.0/1") == "1"
-    assert cidr4_to_binary("0.0.0.0/0") == ""
+    assert cidr4_to_binary("4.78.139.0/24") == "00000100010011101000101100000000"
+    assert cidr4_to_binary("128.0.0.0/1") == "10000000000000000000000000000000"
+    assert cidr4_to_binary("0.0.0.0/0") == "0" * 32
+    assert cidr4_to_binary("0.8.0.0/13") == "00000000000010000000000000000000"
 
-    assert binary_to_cidr4("000001000100111010001011") == "4.78.139.0/24"
-    assert binary_to_cidr4("1") == "128.0.0.0/1"
-    assert binary_to_cidr4("") == "0.0.0.0/0"
+    assert binary_to_cidr4("00000100010011101000101100000000") == "4.78.139.0/24"
+    assert binary_to_cidr4("10000000000000000000000000000000") == "128.0.0.0/1"
+    assert binary_to_cidr4("00000000000000000000000000000000") == "0.0.0.0/0"
+    assert binary_to_cidr4("00000000000010000000000000000000") == "0.8.0.0/13"
 
-    assert reduce_binary("000001000100111010001011") == "00000100010011101000101"
-    assert reduce_binary("1") == ""
-    assert reduce_binary("0") == ""
-    assert reduce_binary("") == ""
-    assert reduce_binary("0001") == ""
-    assert reduce_binary("0000") == ""
+    assert (
+        reduce_binary("00000100010011101000101100000000")
+        == "00000100010011101000101000000000"
+    )
+    assert reduce_binary("10000000000000000000000000000000") == "0" * 32
+    assert reduce_binary("0" * 32) == "0" * 32
+    assert reduce_binary("00000000000010000000000000000000") == "0" * 32
 
     main()