Alternative.

Author: r0f1

README.md

@@ -20,7 +20,7 @@
 |[16](https://adventofcode.com/2020/day/16)|Ticket Translation|[py](/day16/main.py), [alt](/day16/alt.py)|
 |[17](https://adventofcode.com/2020/day/17)|Conway Cubes|[py](/day17/main.py)|
 |[18](https://adventofcode.com/2020/day/18)|Operation Order|[py](/day18/main.py)|
-|[19](https://adventofcode.com/2020/day/19)|Monster Messages|[py](/day19/main.py)|
+|[19](https://adventofcode.com/2020/day/19)|Monster Messages|[py](/day19/main.py), [alt](/day19/alt.py)|
 |[20](https://adventofcode.com/2020/day/20)|-|-|
 |[21](https://adventofcode.com/2020/day/21)|-|-|
 |[22](https://adventofcode.com/2020/day/22)|-|-|

day19/alt.py

@@ -0,0 +1,24 @@
+from lark import Lark, LarkError
+
+def solve(rules, is_part1):
+    if not is_part1:
+        rules = rules.replace('8: 42', '8: 42 | 42 8')
+        rules = rules.replace('11: 42 31', '11: 42 31 | 42 11 31')
+    rules = rules.translate(str.maketrans('0123456789', 'abcdefghij'))
+    parser = Lark(rules, start='a')
+
+    total = 0
+    for line in lines.splitlines():
+        try:
+            parser.parse(line)
+            total += 1
+        except LarkError:
+            pass
+
+    return total
+
+with open("input.txt") as f:
+    rules, lines = [l.rstrip("\n") for l in f.read().split("\n\n")]
+
+for is_part1 in [True, False]:
+    print(solve(rules, is_part1))