day15 part 2 optimized

instead of senselessly trying to find the best starting point, just rely
on the order of neighbor point generation. Since we use a queue
to manage open points and he neighbors are added in the correct
order, they neighbor that has precedence due to reading order will
automatically be the one to be predecessor on a final path, if he is on
a shortest path.

src/main.rs

@@ -1,4 +1,4 @@
 fn main() {
-    aoc_2018::tasks::day15::task1();
-    // aoc_2018::tasks::day15::task2();
+    // aoc_2018::tasks::day15::task1();
+    aoc_2018::tasks::day15::task2();
 }

src/tasks/day15.rs

@@ -4,16 +4,17 @@ use std::collections::HashSet;
 use std::collections::VecDeque;
 use std::fmt::Display;
 
-const ATTACK_POWER: i32 = 3;
 const HEALTH: i32 = 200;
 
 pub fn task1() {
     let input = utils::read_file("input/day15.txt");
-    let mut game = Game::from_input(input.lines().collect());
+    let mut game = Game::from_input(&input.lines().collect(), 3, 3);
     println!("{}", game);
     let mut round = 0;
     while game.round() {
         round += 1;
+        // println!("{}", game);
+        // println!("round was {}", round);
     }
     println!("Final full round was {}", round);
     println!(
@@ -22,6 +23,45 @@ pub fn task1() {
     );
 }
 
+pub fn task2() {
+    let input = utils::read_file("input/day15.txt");
+    let input = input.lines().collect();
+    let mut highest_fail = 3;
+    let mut lowest_win = None::<i32>;
+    while lowest_win.is_none() || lowest_win.unwrap() - 1 > highest_fail {
+        let attack = match lowest_win {
+            Some(upper) => highest_fail + (upper - highest_fail) / 2,
+            None => 2 * highest_fail,
+        };
+        let mut game = Game::from_input(&input, 3, attack);
+        let initial_elve_count = game
+            .units
+            .iter()
+            .filter(|unit| unit.warrior_type == WarriorType::Elve)
+            .count();
+        let mut round = 0;
+        while game.round() {
+            round += 1;
+        }
+        if game
+            .units
+            .iter()
+            .filter(|unit| unit.warrior_type == WarriorType::Elve)
+            .count()
+            == initial_elve_count
+        {
+            lowest_win = Some(attack);
+        } else {
+            highest_fail = attack;
+        }
+        println!(
+            "Result: {}",
+            game.units.iter().map(|it| it.health).sum::<i32>() * round as i32
+        );
+    }
+    println!("Searching stopped with lowest win {:?}", lowest_win); // 7169 too low
+}
+
 #[derive(Clone, PartialEq)]
 enum Tile {
     Empty,
@@ -101,6 +141,7 @@ struct Warrior {
     warrior_type: WarriorType,
     position: Position,
     health: i32,
+    attack: i32,
 }
 
 struct Game {
@@ -136,25 +177,32 @@ impl Game {
         if from == to {
             return Some(from);
         }
-        let input = vec![
-            (1, Position(from.0, from.1 - 1)),
-            (2, Position(from.0 - 1, from.1)),
-            (3, Position(from.0 + 1, from.1)),
-            (4, Position(from.0, from.1 + 1)),
-        ];
-        if let Some((_, best)) = input
-            .iter()
-            .filter_map(|(delta, start)| {
-                let map = Map::from_game(&self, from);
-                if let Some(path) = map.shortest_path(*start, to) {
-                    Some((delta + path.len() * 10, *path.first().unwrap_or(start)))
-                } else {
-                    None
-                }
-            })
-            .min_by_key(|(d, _)| *d)
-        {
-            Some(best)
+        // let input = vec![
+        //     (1, Position(from.0, from.1 - 1)),
+        //     (2, Position(from.0 - 1, from.1)),
+        //     (3, Position(from.0 + 1, from.1)),
+        //     (4, Position(from.0, from.1 + 1)),
+        // ];
+        // if let Some((_, best)) = input
+        //     .iter()
+        //     .filter_map(|(delta, start)| {
+        //         let map = Map::from_game(&self, from);
+        //         if let Some(path) = map.shortest_path(*start, to) {
+        //             Some((delta + path.len() * 10, *path.first().unwrap_or(start)))
+        //         } else {
+        //             None
+        //         }
+        //     })
+        //     .min_by_key(|(d, _)| *d)
+        // {
+        //     Some(best)
+        // } else {
+        //     None
+        // }
+        let map = Map::from_game(&self, from);
+        if let Some(path) = map.shortest_path(from, to) {
+            // println!("{:?}", path);
+            Some(*path.get(1).unwrap_or(&from))
         } else {
             None
         }
@@ -185,6 +233,10 @@ impl Game {
                     if let Some(next_position) =
                         self.next_position(self.units[curr].position, next_target_position)
                     {
+                        // println!(
+                        //     "{:?} moves to {:?} via {:?}",
+                        //     self.units[curr].position, next_target_position, next_position
+                        // );
                         self.units[curr].position = next_position;
                     } else {
                         panic!("We have a reachable target but no path to it! {:?} wants to go to {:?}", self.units[curr], next_target_position);
@@ -219,8 +271,9 @@ impl Game {
                 {
                     panic!("Distance WTF")
                 }
+                let attack = self.units[curr].attack;
                 let enemy = &mut self.units[*closest_index];
-                enemy.health -= ATTACK_POWER;
+                enemy.health -= attack;
                 if enemy.health <= 0 {
                     let enemy = self.units.remove(*closest_index);
                     if *closest_index < curr {
@@ -234,7 +287,7 @@ impl Game {
         return true;
     }
 
-    fn from_input(input: Vec<&str>) -> Self {
+    fn from_input(input: &Vec<&str>, goblin_attack: i32, elve_attack: i32) -> Self {
         use self::Tile::*;
         use self::WarriorType::*;
         let width = input[0].len();
@@ -255,6 +308,7 @@ impl Game {
                             warrior_type: Elve,
                             position: Position(x, y),
                             health: HEALTH,
+                            attack: elve_attack,
                         });
                         Empty
                     }
@@ -263,6 +317,7 @@ impl Game {
                             warrior_type: Goblin,
                             position: Position(x, y),
                             health: HEALTH,
+                            attack: goblin_attack,
                         });
                         Empty
                     }
@@ -391,6 +446,7 @@ impl Map {
         if let Some(Some(_)) = predecessors.get(&to) {
             let mut result: Vec<Position> = Vec::new();
             let mut current = to;
+            result.push(current);
             while let Some(Some(predecessor)) = predecessors.get(&current) {
                 result.push(*predecessor);
                 current = *predecessor;