Solved Day 9 (2015) - All in a Single Night

Author: SimonBaars

src/main/java/com/sbaars/adventofcode/year15/days/Day9.java

@@ -1,23 +1,69 @@
 package com.sbaars.adventofcode.year15.days;
 
 import com.sbaars.adventofcode.year15.Day2015;
+import java.util.*;
+import java.util.stream.Collectors;
 
 public class Day9 extends Day2015 {
+  private final Map<String, Map<String, Integer>> distances = new HashMap<>();
+  private final Set<String> cities = new HashSet<>();
+
   public Day9() {
     super(9);
+    parseInput();
   }
 
   public static void main(String[] args) {
-    new Day9().printParts();
+    Day9 day = new Day9();
+    day.printParts();
+    new com.sbaars.adventofcode.network.Submit().submit(day.part1(), 2015, 9, 1);
+    new com.sbaars.adventofcode.network.Submit().submit(day.part2(), 2015, 9, 2);
+  }
+
+  private void parseInput() {
+    day().lines().forEach(line -> {
+      String[] parts = line.split(" = ");
+      String[] cities = parts[0].split(" to ");
+      int distance = Integer.parseInt(parts[1]);
+      addDistance(cities[0], cities[1], distance);
+      addDistance(cities[1], cities[0], distance);
+      this.cities.add(cities[0]);
+      this.cities.add(cities[1]);
+    });
+  }
+
+  private void addDistance(String from, String to, int distance) {
+    distances.computeIfAbsent(from, k -> new HashMap<>()).put(to, distance);
   }
 
   @Override
   public Object part1() {
-    return "";
+    return findPath(true);
   }
 
   @Override
   public Object part2() {
-    return "";
+    return findPath(false);
+  }
+
+  private int findPath(boolean shortest) {
+    return cities.stream()
+        .mapToInt(start -> findPathFromCity(start, new HashSet<>(List.of(start)), shortest))
+        .reduce(shortest ? Integer.MAX_VALUE : Integer.MIN_VALUE, shortest ? Math::min : Math::max);
+  }
+
+  private int findPathFromCity(String current, Set<String> visited, boolean shortest) {
+    if (visited.size() == cities.size()) {
+      return 0;
+    }
+
+    return distances.get(current).entrySet().stream()
+        .filter(e -> !visited.contains(e.getKey()))
+        .mapToInt(e -> {
+          Set<String> newVisited = new HashSet<>(visited);
+          newVisited.add(e.getKey());
+          return e.getValue() + findPathFromCity(e.getKey(), newVisited, shortest);
+        })
+        .reduce(shortest ? Integer.MAX_VALUE : Integer.MIN_VALUE, shortest ? Math::min : Math::max);
   }
 }