Implement 2024 day 17 part 2

2024/src/aoc/days/day17.py

@@ -3,14 +3,9 @@ import re
 from . import SeparateRunner
 
 
-class DayRunner(SeparateRunner):
-    @classmethod
-    def part1(cls, input: str) -> str:
-        numbers = re.findall(r"\d+", input)
-
-        register_a, register_b, register_c = map(int, numbers[:3])
-        program = list(map(int, numbers[3:]))
-
+def run_program(
+    register_a: int, register_b: int, register_c: int, program: list[int]
+) -> list[int]:
     ip = 0
     out = []
 
@@ -53,8 +48,42 @@ class DayRunner(SeparateRunner):
                 register_c = register_a // 2 ** combo(ip + 1)
         ip += 2
 
+    return out
+
+
+class DayRunner(SeparateRunner):
+    @classmethod
+    def part1(cls, input: str) -> str:
+        numbers = re.findall(r"\d+", input)
+
+        register_a, register_b, register_c = map(int, numbers[:3])
+        program = list(map(int, numbers[3:]))
+
+        out = run_program(register_a, register_b, register_c, program)
+
         return ",".join(map(str, out))
 
     @classmethod
-    def part2(cls, input: str) -> str:
-        pass
+    def part2(cls, input: str) -> int:
+        numbers = re.findall(r"\d+", input)
+
+        _, register_b, register_c = map(int, numbers[:3])
+        program = list(map(int, numbers[3:]))
+
+        cur = [0]
+
+        # It came to me in a dream
+        for entry in reversed(program):
+            next_gen = []
+
+            for num in cur:
+                num *= 8
+                for n in range(8):
+                    output = run_program(num + n, register_b, register_c, program)
+                    result = output[0]
+                    if result == entry:
+                        next_gen.append(num + n)
+
+            cur = next_gen
+
+        return cur[0]

2024/tests/samples/17.2.txt

@@ -0,0 +1,5 @@
+Register A: 2024
+Register B: 0
+Register C: 0
+
+Program: 0,3,5,4,3,0

2024/tests/test_day17.py

@@ -4,4 +4,8 @@ from . import get_data
 
 
 def test_sample_part1() -> None:
-    assert DayRunner.part1(get_data(17)) == "4,6,3,5,6,3,5,2,1,0"
+    assert DayRunner.part1(get_data(17, 1)) == "4,6,3,5,6,3,5,2,1,0"
+
+
+def test_sample_part2() -> None:
+    assert DayRunner.part2(get_data(17, 2)) == 117440