Poor man's trie

Author: bertptrs

2024/src/aoc/days/day19.py

@@ -1,32 +1,37 @@
+import collections
 import functools
 
 from . import CombinedRunner
 
 
-def parse_input(data: str) -> tuple[tuple[str, ...], list[str]]:
+def parse_input(data: str) -> tuple[list[str], list[str]]:
     patterns, designs = data.strip().split("\n\n")
 
-    return tuple(patterns.split(", ")), designs.split("\n")
+    return patterns.split(", "), designs.split("\n")
 
 
 class DayRunner(CombinedRunner):
     @classmethod
     def run_both(cls, input: str) -> int:
         patterns, designs = parse_input(input)
 
+        by_prefix = collections.defaultdict(list)
+        for prefix in patterns:
+            by_prefix[prefix[0]].append(prefix)
+
         possible = 0
         ways = 0
 
         @functools.cache
         def is_possible(design: str) -> bool:
             if not design:
                 return 1
-
-            return sum(
-                is_possible(design[len(pat) :])
-                for pat in patterns
-                if design.startswith(pat)
-            )
+            else:
+                return sum(
+                    is_possible(design[len(prefix) :])
+                    for prefix in by_prefix[design[0]]
+                    if design.startswith(prefix)
+                )
 
         for design in designs:
             if (solve := is_possible(design)) > 0: