2024 day 7.

src/holt59/aoc/2024/day7.py

@@ -3,5 +3,48 @@ from typing import Any, Iterator
 from ..base import BaseSolver
 
 
+def evaluate(
+    target: int, numbers: list[int], concatenate: bool = False, current: int = 0
+) -> bool:
+    if not numbers:
+        return current == target
+
+    if current > target:
+        return False
+
+    head, *tail = numbers
+
+    if evaluate(target, tail, concatenate, current + head) or evaluate(
+        target, tail, concatenate, current * head
+    ):
+        return True
+
+    if not concatenate:
+        return False
+
+    return evaluate(target, tail, concatenate, int(str(current) + str(head)))
+
+
 class Solver(BaseSolver):
-    def solve(self, input: str) -> Iterator[Any]: ...
+    def solve(self, input: str) -> Iterator[Any]:
+        targets = {
+            int(part[0]): list(map(int, part[1].strip().split()))
+            for line in input.splitlines()
+            if (part := line.split(":"))
+        }
+
+        yield sum(
+            target
+            for target, numbers in self.progress.wrap(
+                targets.items(), total=len(targets)
+            )
+            if evaluate(target, numbers)
+        )
+
+        yield sum(
+            target
+            for target, numbers in self.progress.wrap(
+                targets.items(), total=len(targets)
+            )
+            if evaluate(target, numbers, True)
+        )