Day 9 of AOC 2015

Author: Astropilot

README.md

@@ -272,7 +272,7 @@ This repository contains my solutions in Python3 for the [Advent of Code](https:
 |  24 |   ⌛   |   ⌛   |   [🔗](./aoc_2016/day24)   |
 |  25 |   ⌛   |   ⌛   |   [🔗](./aoc_2016/day25)   |
 
-## \[2015] 16⭐
+## \[2015] 18⭐
 
 | Day | Part 1 | Part 2 |         Source link         |
 | :-: | :----: | :----: | :-------------------------: |
@@ -284,7 +284,7 @@ This repository contains my solutions in Python3 for the [Advent of Code](https:
 |  6  |   ⭐   |   ⭐   |   [🔗](./aoc_2015/day6)    |
 |  7  |   ⭐   |   ⭐   |   [🔗](./aoc_2015/day7)    |
 |  8  |   ⭐   |   ⭐   |   [🔗](./aoc_2015/day8)    |
-|  9  |   ⌛   |   ⌛   |   [🔗](./aoc_2015/day9)    |
+|  9  |   ⭐   |   ⭐   |   [🔗](./aoc_2015/day9)    |
 |  10 |   ⌛   |   ⌛   |   [🔗](./aoc_2015/day10)   |
 |  11 |   ⌛   |   ⌛   |   [🔗](./aoc_2015/day11)   |
 |  12 |   ⌛   |   ⌛   |   [🔗](./aoc_2015/day12)   |

aoc_2015/day9/__init__.py

@@ -0,0 +1,40 @@
+from pathlib import Path
+
+with Path(Path(__file__).parent, "input").open() as f:
+    paths = [line.rstrip("\n") for line in f]
+
+NEIGHBORS: dict[str, dict[str, int]] = {}
+
+for path in paths:
+    mapping, distance_raw = path.split(" = ")
+    city_from, city_to = mapping.split(" to ")
+    distance = int(distance_raw)
+
+    d = NEIGHBORS.setdefault(city_from, {})
+    d[city_to] = distance
+
+    d = NEIGHBORS.setdefault(city_to, {})
+    d[city_from] = distance
+
+
+def shortest_distance(city: str, cities: frozenset[str]) -> int:
+    neighbors = frozenset(NEIGHBORS[city].keys())
+    neighbors = neighbors.intersection(cities)
+
+    distances: list[int] = []
+
+    for neighbor in neighbors:
+        available_cities = cities.difference([city, neighbor])
+
+        distances.append(
+            NEIGHBORS[city][neighbor] + shortest_distance(neighbor, available_cities)
+        )
+
+    return min(distances) if len(distances) > 0 else 0
+
+
+cities = frozenset(NEIGHBORS.keys())
+
+result = min(shortest_distance(city, cities) for city in cities)
+
+print(f"Result: {result}")

aoc_2015/day9/part1.py

@@ -0,0 +1,40 @@
+from pathlib import Path
+
+with Path(Path(__file__).parent, "input").open() as f:
+    paths = [line.rstrip("\n") for line in f]
+
+NEIGHBORS: dict[str, dict[str, int]] = {}
+
+for path in paths:
+    mapping, distance_raw = path.split(" = ")
+    city_from, city_to = mapping.split(" to ")
+    distance = int(distance_raw)
+
+    d = NEIGHBORS.setdefault(city_from, {})
+    d[city_to] = distance
+
+    d = NEIGHBORS.setdefault(city_to, {})
+    d[city_from] = distance
+
+
+def shortest_distance(city: str, cities: frozenset[str]) -> int:
+    neighbors = frozenset(NEIGHBORS[city].keys())
+    neighbors = neighbors.intersection(cities)
+
+    distances: list[int] = []
+
+    for neighbor in neighbors:
+        available_cities = cities.difference([city, neighbor])
+
+        distances.append(
+            NEIGHBORS[city][neighbor] + shortest_distance(neighbor, available_cities)
+        )
+
+    return max(distances) if len(distances) > 0 else 0
+
+
+cities = frozenset(NEIGHBORS.keys())
+
+result = max(shortest_distance(city, cities) for city in cities)
+
+print(f"Result: {result}")