feat(09/2015): solve second part

Author: manhunto

readme.md

@@ -95,7 +95,7 @@
 | [Day 6: Probably a Fire Hazard](src/solutions/year2015/day06.rs)                 |   ⭐⭐   |          871.538 |          817.533 |
 | [Day 7: Some Assembly Required](src/solutions/year2015/day07.rs)                 |   ⭐⭐   |            0.308 |            0.293 |
 | [Day 8: Matchsticks](src/solutions/year2015/day08.rs)                            |   ⭐⭐   |            0.052 |            0.129 |
-| [Day 9: All in a Single Night](src/solutions/year2015/day09.rs)                  |   ⭐    |           34.320 |                - |
+| [Day 9: All in a Single Night](src/solutions/year2015/day09.rs)                  |   ⭐⭐   |           34.320 |            34.85 |
 
 # TODO
 

src/solutions/year2015/day09.rs

@@ -12,8 +12,11 @@ impl Solution for Day09 {
             .to_string()
     }
 
-    fn part_two(&self, _input: &str) -> String {
-        String::from("0")
+    fn part_two(&self, input: &str) -> String {
+        self.parse(input)
+            .find_longest_path_cost()
+            .unwrap()
+            .to_string()
     }
 }
 
@@ -47,4 +50,9 @@ Dublin to Belfast = 141"#;
     fn part_one_example_test() {
         assert_eq!("605", Day09.part_one(EXAMPLE));
     }
+
+    #[test]
+    fn part_two_example_test() {
+        assert_eq!("982", Day09.part_two(EXAMPLE));
+    }
 }

src/utils/graphs/graph.rs

@@ -66,7 +66,7 @@ impl<T> Graph<T> {
     fn edges(&self) -> &HashSet<(T, T)> {
         &self.edges
     }
-    
+
     pub fn nodes(&self) -> &HashSet<T> {
         &self.nodes
     }

src/utils/graphs/travelling_salesman.rs

@@ -19,18 +19,32 @@ impl<T: PartialEq + Eq + Hash> TravellingSalesman<T> {
     }
 
     pub fn find_shortest_path_cost(&self) -> Option<usize>
+    where
+        T: PartialEq + Clone,
+    {
+        self.all_paths().iter().map(|path| path.cost).min()
+    }
+
+    pub fn find_longest_path_cost(&self) -> Option<usize>
+    where
+        T: PartialEq + Clone,
+    {
+        self.all_paths().iter().map(|path| path.cost).max()
+    }
+
+    fn all_paths(&self) -> Vec<Path<T>>
     where
         T: PartialEq + Clone,
     {
         self.graph
             .nodes()
             .iter()
             .tuple_combinations()
-            .map(|(from, to)| self.shortest_path(from, to))
-            .min()
+            .flat_map(|(from, to)| self.all_paths_between(from, to))
+            .collect()
     }
 
-    fn shortest_path(&self, from: &T, to: &T) -> usize
+    fn all_paths_between(&self, from: &T, to: &T) -> Vec<Path<T>>
     where
         T: PartialEq + Clone,
     {
@@ -64,7 +78,7 @@ impl<T: PartialEq + Eq + Hash> TravellingSalesman<T> {
             }
         }
 
-        finished_paths.iter().map(|path| path.cost).min().unwrap()
+        finished_paths
     }
 }