2016: d07: ex2: add solution

2016/d07/ex2/ex2.py

@@ -0,0 +1,52 @@
+#!/usr/bin/env python
+
+import itertools
+import sys
+from collections.abc import Iterator
+
+
+def solve(input: str) -> int:
+    def iter_aba(input: str) -> Iterator[tuple[str, str]]:
+        for i in range(3, len(input) + 1):
+            a, b, c = (input[i - j] for j in range(3, 0, -1))
+            if a == b:
+                continue
+            if a != c:
+                continue
+            yield a, b
+
+    def split_address(address) -> tuple[list[str], list[str]]:
+        nets: tuple[list[str], list[str]] = [], []
+        i = 0
+        is_hypernet = False
+        while i < len(address):
+            if is_hypernet:
+                j = address.find("]", i)
+            else:
+                j = address.find("[", i)
+            if j == -1:
+                j = len(address)
+            nets[is_hypernet].append(address[i:j])
+            i = j
+            is_hypernet = not is_hypernet
+        return nets
+
+    def supports_ssl(address: str) -> bool:
+        supernets, hypernets = split_address(address)
+        aba_candidates = itertools.chain.from_iterable(map(iter_aba, supernets))
+        for a, b in aba_candidates:
+            bab = b + a + b
+            if any(bab in net for net in hypernets):
+                return True
+        return False
+
+    return sum(map(supports_ssl, input.splitlines()))
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()