2020 day 19 and day 20 part 1

2020/d19.py

@@ -0,0 +1,62 @@
+from lib import get_data
+
+data = get_data(__file__)
+
+rules = {}
+msgs = []
+
+for line in data.splitlines():
+    if len(line.strip()) == 0:
+        continue
+
+    if ":" in line:
+        id, rule = line.split(":")
+        id = int(id)
+
+        branches = [[]]
+        for part in rule.split():
+            if part.startswith('"') and part.endswith('"'):
+                branches = part[1]
+            elif part == "|":
+                assert type(branches) is list
+                branches.append([])
+            else:
+                assert type(branches) is list
+                branches[-1].append(int(part))
+        rules[id] = branches
+    else:
+        msgs.append(line.strip())
+
+
+def matches(xs, rule):
+    if xs == "" and rule == []:
+        return True
+    elif xs == "" or rule == []:
+        return False
+
+    current = rules[rule[0]]
+    if current == xs[0]:
+        return matches(xs[1:], rule[1:])
+    elif type(current) is str:
+        return False
+    elif len(current) >= 1:
+        for ys in current:
+            if matches(xs, ys + rule[1:]):
+                return True
+    return False
+
+
+t = 0
+for m in msgs:
+    if matches(m, rules[0][0]):
+        t += 1
+print(t)
+
+rules[8] = [[42], [42, 8]]
+rules[11] = [[42, 31], [42, 11, 31]]
+
+t = 0
+for m in msgs:
+    if matches(m, rules[0][0]):
+        t += 1
+print(t)