Day 25 of AOC 2017

Author: Astropilot

README.md

@@ -212,7 +212,7 @@ This repository contains my solutions in Python3 for the [Advent of Code](https:
 |  24 |   ⌛   |   ⌛   |   [🔗](./aoc_2018/day24)   |
 |  25 |   ⌛   |   ⌛   |   [🔗](./aoc_2018/day25)   |
 
-## \[2017] 48⭐
+## \[2017] 50⭐
 
 | Day | Part 1 | Part 2 |         Source link         |
 | :-: | :----: | :----: | :-------------------------: |
@@ -240,7 +240,7 @@ This repository contains my solutions in Python3 for the [Advent of Code](https:
 |  22 |   ⭐   |   ⭐   |   [🔗](./aoc_2017/day22)   |
 |  23 |   ⭐   |   ⭐   |   [🔗](./aoc_2017/day23)   |
 |  24 |   ⭐   |   ⭐   |   [🔗](./aoc_2017/day24)   |
-|  25 |   ⌛   |   ⌛   |   [🔗](./aoc_2017/day25)   |
+|  25 |   ⭐   |   ⭐   |   [🔗](./aoc_2017/day25)   |
 
 ## \[2016] 18⭐
 

aoc_2017/day25/__init__.py

@@ -0,0 +1,64 @@
+import re
+import typing as t
+from dataclasses import dataclass
+from pathlib import Path
+
+
+@dataclass
+class State:
+    name: str
+    action_if_0: tuple[t.Literal[0, 1], t.Literal[1, -1], str]
+    action_if_1: tuple[t.Literal[0, 1], t.Literal[1, -1], str]
+
+
+with Path(Path(__file__).parent, "input").open() as f:
+    instructions = [line.rstrip("\n") for line in f]
+
+begin_state = instructions[0][-2]
+steps_stop = int(re.search(r"\d+", instructions[1]).group(0))  # type: ignore
+states: dict[str, State] = {}
+tape: list[t.Literal[0, 1]] = [0]
+cursor = 0
+
+
+def move_cursor(tape: list[t.Literal[0, 1]], cursor: int) -> int:
+    if cursor == -1:
+        tape.insert(0, 0)
+        return 0
+    elif cursor == len(tape):
+        tape.append(0)
+    return cursor
+
+
+for i in range(3, len(instructions), 10):
+    state_name = instructions[i][-2]
+    action_if_0 = (
+        int(instructions[i + 2][-2]),
+        -1
+        if instructions[i + 3].removeprefix("    - Move one slot to the ")[:-1]
+        == "left"
+        else 1,
+        instructions[i + 4][-2],
+    )
+    action_if_1 = (
+        int(instructions[i + 6][-2]),
+        -1
+        if instructions[i + 7].removeprefix("    - Move one slot to the ")[:-1]
+        == "left"
+        else 1,
+        instructions[i + 8][-2],
+    )
+    states[state_name] = State(state_name, action_if_0, action_if_1)  # type: ignore
+
+current_state = states[begin_state]
+
+for _ in range(steps_stop):
+    action = (
+        current_state.action_if_0 if tape[cursor] == 0 else current_state.action_if_1
+    )
+
+    tape[cursor] = action[0]
+    cursor = move_cursor(tape, cursor + action[1])
+    current_state = states[action[2]]
+
+print(f"Result: {sum(tape)}")