Day 17: Chronospatial Computer

README.md

@@ -21,4 +21,4 @@ Development occurs in language-specific directories:
 |[Day14.hs](hs/src/Day14.hs)|[Day14.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day14.kt)|[day14.py](py/aoc2024/day14.py)|[day14.rs](rs/src/day14.rs)|
 |[Day15.hs](hs/src/Day15.hs)|[Day15.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day15.kt)|[day15.py](py/aoc2024/day15.py)|[day15.rs](rs/src/day15.rs)|
 |[Day16.hs](hs/src/Day16.hs)|[Day16.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day16.kt)|[day16.py](py/aoc2024/day16.py)|[day16.rs](rs/src/day16.rs)|
-|[Day17.hs](hs/src/Day17.hs)|[Day17.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day17.kt)|||
+|[Day17.hs](hs/src/Day17.hs)|[Day17.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day17.kt)|[day17.py](py/aoc2024/day17.py)||

py/aoc2024/day17.py

@@ -0,0 +1,100 @@
+"""
+Day 17: Chronospatial Computer
+"""
+
+import re
+import sys
+from typing import Generator
+
+SAMPLE_INPUT_1 = """
+Register A: 729
+Register B: 0
+Register C: 0
+
+Program: 0,1,5,4,3,0
+"""
+SAMPLE_INPUT_2 = """
+Register A: 2024
+Register B: 0
+Register C: 0
+
+Program: 0,3,5,4,3,0
+"""
+
+_pattern = re.compile(r"A: (\d+)|B: (\d+)|C: (\d+)|Program: ([\d,]*)")
+
+
+def _parse(data: str) -> tuple[int, int, int, list[int]]:
+    a, b, c, program = 0, 0, 0, []
+    for match in _pattern.finditer(data):
+        if capture := match.group(1):
+            a = int(capture)
+        elif capture := match.group(2):
+            b = int(capture)
+        elif capture := match.group(3):
+            c = int(capture)
+        else:
+            program = [int(num) for num in match.group(4).split(",")]
+    return a, b, c, program
+
+
+def _run(a: int, b: int, c: int, program: list[int]) -> Generator[int]:
+    ip = 0
+    while 0 <= ip and ip + 1 < len(program):
+        instruction = program[ip]
+        operand = program[ip + 1]
+        combo = (0, 1, 2, 3, a, b, c)[operand] if 0 <= operand < 7 else None
+        match instruction:
+            case 0:
+                a = a >> combo
+            case 1:
+                b = b ^ operand
+            case 2:
+                b = combo & 7
+            case 3:
+                if a:
+                    ip = operand
+                    continue
+            case 4:
+                b = b ^ c
+            case 5:
+                yield combo & 7
+            case 6:
+                b = a >> combo
+            case 7:
+                c = a >> combo
+            case _:
+                raise NotImplementedError()
+        ip += 2
+
+
+def part1(data: str) -> str:
+    """
+    >>> part1(SAMPLE_INPUT_1)
+    '4,6,3,5,6,3,5,2,1,0'
+    """
+    a, b, c, program = _parse(data)
+    return ",".join(map(str, _run(a, b, c, program)))
+
+
+def part2(data: str) -> int:
+    """
+    >>> part2(SAMPLE_INPUT_2)
+    117440
+    """
+    a, b, c, program = _parse(data)
+    expected = ",".join(map(str, program))
+    candidates = [0]
+    while candidates:
+        keys = [8 * a + b for a in candidates for b in range(8)]
+        candidates.clear()
+        for a in keys:
+            value = ",".join(map(str, _run(a, b, c, program)))
+            if value == expected:
+                return a
+            if expected.endswith("," + value):
+                candidates.append(a)
+    return None
+
+
+parts = (part1, part2)

py/pyproject.toml

@@ -40,6 +40,7 @@ day13 = "aoc2024.day13:parts"
 day14 = "aoc2024.day14:parts"
 day15 = "aoc2024.day15:parts"
 day16 = "aoc2024.day16:parts"
+day17 = "aoc2024.day17:parts"
 
 [build-system]
 requires = ["poetry-core"]