Fix problem by adding more lookback

2024/bonus/24todot.py

@@ -0,0 +1,15 @@
+import fileinput
+
+print("digraph day24 {")
+
+for line in fileinput.input():
+    parts = line.split(" ")
+    if len(parts) != 5:
+        continue
+
+    first, op, second, _, result = parts
+    print(f'{first}{second}{op} [label="{op}"];')
+    print(f"{first} -> {first}{second}{op} -> {result};")
+    print(f"{second} -> {first}{second}{op};")
+
+print("}")

2024/src/aoc/days/day24.py

@@ -0,0 +1,133 @@
+import functools
+import re
+
+from . import SeparateRunner
+
+
+def parse_input(input: str) -> tuple[dict[str, int], dict[str, tuple[str, str, str]]]:
+    variable_part, rules_part = input.strip().split("\n\n")
+
+    variables = {}
+
+    for line in variable_part.splitlines():
+        variable, value = line.split(": ")
+        variables[variable] = int(value)
+
+    rules = {}
+
+    for first, op, second, result in re.findall(
+        r"(\w+) (XOR|OR|AND) (\w+) -> (\w+)", rules_part
+    ):
+        rules[result] = (first, op, second)
+
+    return variables, rules
+
+
+class DayRunner(SeparateRunner):
+    @classmethod
+    def part1(cls, input: str) -> int:
+        variables, rules = parse_input(input)
+
+        @functools.cache
+        def get_value(variable: str) -> int:
+            if variable in variables:
+                return variables[variable]
+
+            first, op, second = rules[variable]
+            first_v = get_value(first)
+            second_v = get_value(second)
+
+            match op:
+                case "AND":
+                    return first_v & second_v
+                case "OR":
+                    return first_v | second_v
+                case "XOR":
+                    return first_v ^ second_v
+
+        result = 0
+        for variable in reversed(sorted(rules)):
+            if not variable.startswith("z"):
+                continue
+            result = result * 2 + get_value(variable)
+
+        return result
+
+    @classmethod
+    def part2(cls, input: str) -> str:
+        variables, rules = parse_input(input)
+
+        max_bit = int(
+            max(variable for variable in rules if variable.startswith("z"))[1:]
+        )
+
+        def find_invalid(output: str, pattern) -> set[str]:
+            if pattern is None:
+                return set()
+
+            if output in rules:
+                left, op, right = rules[output]
+            elif output == pattern:
+                return set()
+            else:
+                return {output}
+
+            pop, pleft, pright = pattern
+
+            if op != pop:
+                return {output}
+
+            wrong_normal = find_invalid(left, pleft) | find_invalid(right, pright)
+            wrong_mirror = find_invalid(left, pright) | find_invalid(right, pleft)
+
+            least_wrong = min(wrong_mirror, wrong_normal, key=len)
+
+            return least_wrong
+
+        assert max_bit >= 3
+
+        # First one is a half adder, that's a simple pattern
+        invalid = find_invalid("z00", ["XOR", "x00", "y00"])
+        # Second one is missing a reference to the before-previous adder, so it's a
+        # slightly different patterns
+        invalid |= find_invalid(
+            "z01", ["XOR", ["AND", "x00", "y00"], ["XOR", "x01", "y01"]]
+        )
+        # Needed a second lookback to determine that `ktp` is valid
+        invalid |= find_invalid(
+            "z02",
+            [
+                "XOR",
+                ["XOR", "x02", "y02"],
+                [
+                    "OR",
+                    ["AND", "x01", "y01"],
+                    ["AND", ["XOR", "x01", "y01"], ["AND", "x00", "y00"]],
+                ],
+            ],
+        )
+
+        for n in range(3, max_bit):
+            xcurr = f"x{n:02}"
+            ycurr = f"y{n:02}"
+            zcurr = f"z{n:02}"
+            xprev = f"x{n-1:02}"
+            yprev = f"y{n-1:02}"
+
+            invalid |= find_invalid(
+                zcurr,
+                [
+                    "XOR",
+                    ["XOR", xcurr, ycurr],
+                    [
+                        "OR",
+                        ["AND", xprev, yprev],
+                        ["AND", ["XOR", xprev, yprev], ["OR", None, None]],
+                    ],
+                ],
+            )
+
+        # This code somehow believes `ktp` is invalid, but it's fine on closer
+        # inspection. Will figure that out later.
+
+        return ",".join(sorted(invalid))

2024/tests/samples/24.txt

@@ -0,0 +1,47 @@
+x00: 1
+x01: 0
+x02: 1
+x03: 1
+x04: 0
+y00: 1
+y01: 1
+y02: 1
+y03: 1
+y04: 1
+
+ntg XOR fgs -> mjb
+y02 OR x01 -> tnw
+kwq OR kpj -> z05
+x00 OR x03 -> fst
+tgd XOR rvg -> z01
+vdt OR tnw -> bfw
+bfw AND frj -> z10
+ffh OR nrd -> bqk
+y00 AND y03 -> djm
+y03 OR y00 -> psh
+bqk OR frj -> z08
+tnw OR fst -> frj
+gnj AND tgd -> z11
+bfw XOR mjb -> z00
+x03 OR x00 -> vdt
+gnj AND wpb -> z02
+x04 AND y00 -> kjc
+djm OR pbm -> qhw
+nrd AND vdt -> hwm
+kjc AND fst -> rvg
+y04 OR y02 -> fgs
+y01 AND x02 -> pbm
+ntg OR kjc -> kwq
+psh XOR fgs -> tgd
+qhw XOR tgd -> z09
+pbm OR djm -> kpj
+x03 XOR y03 -> ffh
+x00 XOR y04 -> ntg
+bfw OR bqk -> z06
+nrd XOR fgs -> wpb
+frj XOR qhw -> z04
+bqk OR frj -> z07
+y03 OR x01 -> nrd
+hwm AND bqk -> z03
+tgd XOR rvg -> z12
+tnw OR pbm -> gnj

2024/tests/test_day24.py

@@ -0,0 +1,7 @@
+from aoc.days.day24 import DayRunner
+
+from . import get_data
+
+
+def test_sample_part1() -> None:
+    assert DayRunner.part1(get_data(24)) == 2024