2017: d18: ex1: add solution

2017/d18/ex1/ex1.py

@@ -0,0 +1,76 @@
+#!/usr/bin/env python
+
+import collections
+import enum
+import sys
+from typing import NamedTuple
+
+
+class Op(enum.StrEnum):
+    SND = "snd"
+    SET = "set"
+    ADD = "add"
+    MUL = "mul"
+    MOD = "mod"
+    RCV = "rcv"
+    JGZ = "jgz"
+
+
+class Instruction(NamedTuple):
+    op: Op
+    x: str
+    y: str | None = None
+
+    @classmethod
+    def from_str(cls, input: str) -> "Instruction":
+        op, *rest = input.split()
+        return cls(Op(op), *rest)
+
+
+def solve(input: str) -> int:
+    def parse(input: str) -> list[Instruction]:
+        return [Instruction.from_str(line) for line in input.splitlines()]
+
+    def resolve(y: str | None, registers: dict[str, int]) -> int:
+        assert y is not None  # Sanity check
+        try:
+            return int(y)
+        except ValueError:
+            return registers[y]
+
+    instructions = parse(input)
+    registers: dict[str, int] = collections.defaultdict(int)
+
+    ip = 0
+    freq: int | None = None
+    while True:
+        assert 0 <= ip < len(instructions)  # Sanity check
+        instr = instructions[ip]
+        ip += 1
+        match instr.op:
+            case Op.SND:
+                freq = resolve(instr.x, registers)
+            case Op.SET:
+                registers[instr.x] = resolve(instr.y, registers)
+            case Op.ADD:
+                registers[instr.x] += resolve(instr.y, registers)
+            case Op.MUL:
+                registers[instr.x] *= resolve(instr.y, registers)
+            case Op.MOD:
+                registers[instr.x] %= resolve(instr.y, registers)
+            case Op.RCV:
+                if resolve(instr.x, registers) != 0:
+                    assert freq is not None
+                    return freq
+            case Op.JGZ:
+                if resolve(instr.x, registers) > 0:
+                    ip += resolve(instr.y, registers) - 1  # Account auto-increment
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()