Day 07

07.py

@@ -0,0 +1,26 @@
+#!/usr/bin/python3
+
+import re
+
+# Returns True if x contains an ABBA sequence
+abba = lambda x: re.match(r'.*(.)(?!\1)(.)\2\1.*', x)
+# Returns all trigrams in x
+tris = lambda x: [x[i:i+3] for i in range(len(x) - 2) if '#' not in x[i:i+3]]
+# Returns all ABA sequences in x
+abas = lambda x: [t for t in tris(x) if t[0] == t[2] and t[1] != t[0]]
+# Swaps an ABA trigram into BAB
+swap = lambda x: x[1] + x[0] + x[1]
+# Returns all hypernet parts (between brackets) of x
+hypernet = lambda x: re.sub(r'^.*?\[|\].*?\[|\].*?$', '#', x)
+# Returns all supernet parts (outside of brackets) of x
+supernet = lambda x: re.sub(r'\[.*?\]', '#', x)
+
+with open('07.txt', 'r') as file:
+    ips = list(map(str.strip, file.readlines()))
+    # tls: has at least one ABBA that's not also in its hypernet sections
+    tls = set(filter(abba, ips)) - set(filter(lambda ip: abba(hypernet(ip)), ips))
+    # ssl: has an ABA in the supernet and a BAB in the hypernet
+    ssl = [ip for ip in ips if set(map(swap, abas(supernet(ip)))).intersection(set(abas(hypernet(ip))))]
+    
+    print("Part one: %s" % len(tls))
+    print("Part two: %s" % len(ssl))