2024: Day 17

Author: MiLk

2024/python/day17/__init__.py

@@ -0,0 +1,69 @@
+import sys
+
+from utils.file import read_input
+
+lines = read_input(__package__)
+registers = int(lines[0][12:]), int(lines[1][12:]), int(lines[2][12:])
+program = tuple(map(int, lines[3][9:].split(",")))
+end = len(program)
+
+
+def run_program(ra: int, rb: int, rc: int) -> tuple[int, ...]:
+    def combo(value: int) -> int:
+        match value:
+            case 4:
+                return ra
+            case 5:
+                return rb
+            case 6:
+                return rc
+            case 0 | 1 | 2 | 3:
+                return value
+            case _:
+                raise ValueError(f"Invalid operand {value}")
+
+    iptr = 0
+    output: list[int] = []
+    while iptr < end:
+        opcode, operand = program[iptr], program[iptr + 1]
+        match opcode:
+            case 0:  # adv
+                ra = ra // 2 ** combo(operand)
+            case 1:  # bxl
+                rb = rb ^ operand
+            case 2:  # bst
+                rb = combo(operand) % 8
+            case 3 if ra != 0:  # jnz
+                iptr = operand
+                continue
+            case 3:
+                pass
+            case 4:  # bxc
+                rb = rb ^ rc
+            case 5:  # out
+                output.append(combo(operand) % 8)
+            case 6:  # bdv
+                rb = ra // 2 ** combo(operand)
+            case 7:  # cdv
+                rc = ra // 2 ** combo(operand)
+            case _:
+                return tuple()
+        iptr += 2
+    return tuple(output)
+
+
+print("Part 1:", ",".join(map(str, run_program(*registers))))
+
+
+def find_input(cursor: int, seed: int) -> int | None:
+    for candidate in range(8):
+        if run_program(seed * 8 + candidate, registers[1], registers[2]) != program[cursor:]:
+            continue
+        if cursor == 0:
+            return seed * 8 + candidate
+        if (result := find_input(cursor - 1, seed * 8 + candidate)) is not None:
+            return result
+    return None
+
+
+print("Part 2:", find_input(len(program) - 1, 0))

2024/python/day17/__main__.py

@@ -0,0 +1,14 @@
+Register A: 30878003
+Register B: 0
+Register C: 0
+
+Program: 2,4,1,2,7,5,0,3,4,7,1,7,5,5,3,0
+
+while ra != 0:
+    rb = ra % 8
+    rb = rb ^ 2
+    rc = ra / rb
+    ra = ra / 3
+    rb = rb ^ rc
+    rb = rb ^ 7
+    out (rb % 8)