Partial solution for day 15 part 1.

Partial in the sense that it doesn't actually work for my input, only
for the samples.

2018/inputs/15.txt

@@ -0,0 +1,32 @@
+################################
+################.#.#..##########
+################.#...G##########
+################...#############
+######..##########.#..##########
+####.G...#########.G...#########
+###.........######....##########
+##..#.##.....#....#....#########
+#G.#GG..................##.#####
+##.##..##..G........G.........##
+#######......G.G...............#
+#######........................#
+########.G....#####..E#...E.G..#
+#########G...#######...........#
+#########...#########.........##
+#####.......#########....G...###
+###.........#########.....E..###
+#...........#########.........##
+#..#....G..G#########........###
+#..#.........#######.........###
+#G.##G......E.#####...E..E..####
+##......E...............########
+#.....#G.G..............E..#####
+#....#####....E........###.#####
+#...#########.........####.#####
+#.###########......#.#####.#####
+#....##########.##...###########
+#....#############....##########
+##.##############E....##########
+##.##############..#############
+##....##########################
+################################

2018/src/common.rs

@@ -3,6 +3,8 @@ use std::hash::Hash;
 use std::io;
 use std::io::Read;
 use std::str::FromStr;
+use std::ops::Add;
+use std::ops::Sub;
 
 /// Apply Erathostenes's sieve to the supplied array
 ///
@@ -65,6 +67,15 @@ pub fn read_single_input<T>(input: &mut Read) -> T
     buf.trim().parse().unwrap()
 }
 
+/// Compute the manhattan distance between two points of arbitrary type.
+pub fn manhattan_distance<T>(a: (T, T), b: (T, T)) -> T
+where T: Copy + Add<Output=T> + Sub<Output=T> + Ord
+{
+    let (xa, ya) = a;
+    let (xb, yb) = b;
+    xa.max(xb) + ya.max(yb) - xa.min(xb) - ya.min(yb)
+}
+
 
 /// An interface to count elements in particular categories.
 pub trait GroupingCount {

2018/src/day15.rs

@@ -1,19 +1,228 @@
+use std::collections::HashMap;
+use std::collections::HashSet;
+use std::collections::VecDeque;
+use std::io::BufRead;
+use std::io::BufReader;
 use std::io::Read;
 
+use common::manhattan_distance;
 use common::Solution;
 
+type Coordinate = (usize, usize);
+
+#[derive(Debug, Eq, PartialEq, Ord, PartialOrd)]
+struct Unit {
+    pos: Coordinate,
+    hp: u8,
+    power: u8,
+    faction: char,
+}
+
+impl Default for Unit {
+    fn default() -> Self {
+        Unit {
+            pos: (0, 0),
+            hp: 200,
+            power: 3,
+            faction: 'E',
+        }
+    }
+}
+
+impl Unit {
+    pub fn is_alive(&self) -> bool {
+        self.hp > 0
+    }
+}
+
 #[derive(Default)]
-pub struct Day15 {}
+pub struct Day15 {
+    walls: Vec<Vec<bool>>,
+    units: Vec<Unit>,
+    alive: [usize; 2],
+}
 
 impl Day15 {
     pub fn new() -> Self {
         Default::default()
     }
+
+    fn read_input(&mut self, input: &mut Read) {
+        let reader = BufReader::new(input);
+
+        for (y, line) in reader.lines().enumerate() {
+            let line = line.unwrap();
+            let mut current = vec![false; line.len()];
+
+            for (x, c) in line.chars().enumerate() {
+                match c {
+                    '#' => { current[x] = true; }
+                    'G' => {
+                        self.units.push(Unit {
+                            pos: (y, x),
+                            faction: 'G',
+                            ..Default::default()
+                        });
+                        self.alive[1] += 1;
+                    }
+                    'E' => {
+                        self.units.push(Unit {
+                            pos: (y, x),
+                            ..Default::default()
+                        });
+                        self.alive[0] += 1;
+                    }
+                    '.' => {}
+                    c => panic!("Invalid tile {}!", c),
+                }
+            }
+            self.walls.push(current);
+        }
+    }
+
+    fn get_movement(&self, unit: usize) -> Option<Coordinate> {
+        let initial = self.units[unit].pos;
+        let faction = self.units[unit].faction;
+
+        let positions: HashSet<Coordinate> = self.units.iter()
+            .filter(|x| x.faction != faction && x.is_alive())
+            .map(|x| x.pos).collect();
+
+        let all_positions: HashSet<Coordinate> = self.units.iter()
+            .filter(|x| x.is_alive())
+            .map(|x| x.pos).collect();
+
+        let mut todo = VecDeque::new();
+        let mut prev = HashMap::new();
+
+        todo.push_back(initial);
+
+        while let Some((y, x)) = todo.pop_front() {
+            let next = [
+                (y - 1, x),
+                (y, x - 1),
+                (y, x + 1),
+                (y + 1, x),
+            ];
+
+            for pos in &next {
+                if !prev.contains_key(pos) && !self.walls[pos.0][pos.1] {
+                    prev.insert(*pos, (y, x));
+                    if positions.contains(pos) {
+                        if (y, x) == initial {
+                            return None;
+                        }
+
+                        let mut next_pos = *pos;
+                        // Found the nearest enemy
+                        while let Some(prev_pos) = prev.get(&next_pos) {
+                            if *prev_pos != initial {
+                                next_pos = *prev_pos;
+                            } else {
+                                break;
+                            }
+                        }
+
+                        return Some(next_pos);
+                    } else if !all_positions.contains(pos) {
+                        todo.push_back(*pos);
+                    }
+                }
+            }
+        }
+        None
+    }
+
+    fn get_attack(&self, unit: usize) -> Option<usize> {
+        let initial = self.units[unit].pos;
+        let faction = self.units[unit].faction;
+
+        let to_attack = self.units.iter()
+            .enumerate()
+            .filter(|(_, x)| x.faction != faction && x.is_alive())
+            .filter(|(_, x)| manhattan_distance(x.pos, initial) == 1)
+            .min_by(|&(_, a), &(_, b)| a.hp.cmp(&b.hp).then(a.pos.cmp(&b.pos)));
+
+        if let Some((index, _)) = to_attack {
+            Some(index)
+        } else {
+            None
+        }
+    }
+
+    fn simulate(&mut self) -> bool {
+        self.units.sort_unstable();
+        for i in 0..self.units.len() {
+            if !self.units[i].is_alive() {
+                continue;
+            }
+
+            if self.alive[0] == 0 || self.alive[1] == 0 {
+                return false;
+            }
+
+            if let Some(new_pos) = self.get_movement(i) {
+                self.units[i].pos = new_pos;
+            }
+
+            if let Some(target) = self.get_attack(i) {
+                let power = self.units[i].power;
+                let target = &mut self.units[target];
+                target.hp = target.hp.saturating_sub(power);
+
+                if target.hp == 0 {
+                    match target.faction {
+                        'E' => { self.alive[0] -= 1 }
+                        'G' => { self.alive[1] -= 1 },
+                        _ => panic!(),
+                    };
+                }
+            }
+        }
+
+        true
+    }
+
+    #[allow(dead_code)]
+    fn print(&self) {
+        let positions: HashMap<_, _> = self.units.iter()
+            .filter(|x| x.is_alive())
+            .map(|x| (x.pos, x))
+            .collect();
+
+        for y in 0..self.walls.len() {
+            let mut buf = String::new();
+            let mut unit_buf = String::new();
+
+            for x in 0..self.walls[y].len() {
+                if let Some(unit) = positions.get(&(y, x)) {
+                    buf.push(unit.faction);
+
+                    unit_buf += &format!("    {}({})", unit.faction, unit.hp);
+                } else if self.walls[y][x] {
+                    buf.push('#');
+                } else {
+                    buf.push('.');
+                }
+            }
+            println!("{}{}", buf, unit_buf);
+        }
+    }
 }
 
 impl Solution for Day15 {
-    fn part1(&mut self, _input: &mut Read) -> String {
-        unimplemented!()
+    fn part1(&mut self, input: &mut Read) -> String {
+        self.read_input(input);
+        let mut rounds = 0;
+        while self.simulate() {
+            rounds += 1;
+            //println!("Result after round {}: ", rounds);
+            //self.print();
+        }
+        let result: usize = rounds * self.units.iter().map(|x| x.hp as usize)
+            .sum::<usize>();
+
+        format!("{}", result)
     }
 
     fn part2(&mut self, _input: &mut Read) -> String {
@@ -22,4 +231,33 @@ impl Solution for Day15 {
 }
 
 #[cfg(test)]
-mod tests {}
+mod tests {
+    use common::Solution;
+    use day15::Day15;
+
+    const SAMPLE_INPUT: [&[u8]; 6] = [
+        include_bytes!("samples/15.1.txt"),
+        include_bytes!("samples/15.2.txt"),
+        include_bytes!("samples/15.3.txt"),
+        include_bytes!("samples/15.4.txt"),
+        include_bytes!("samples/15.5.txt"),
+        include_bytes!("samples/15.6.txt"),
+    ];
+
+    const SAMPLE_OUTPUT: [&str; 6] = [
+        "27730",
+        "36334",
+        "39514",
+        "27755",
+        "28944",
+        "18740",
+    ];
+
+    #[test]
+    fn sample_part1() {
+        for (input, output) in SAMPLE_INPUT.iter().zip(SAMPLE_OUTPUT.iter()) {
+            let mut instance = Day15::new();
+            assert_eq!(*output, instance.part1(&mut input.as_ref()));
+        }
+    }
+}

2018/src/samples/15.1.txt

@@ -0,0 +1,7 @@
+#######
+#.G...#
+#...EG#
+#.#.#G#
+#..G#E#
+#.....#
+#######

2018/src/samples/15.2.txt

@@ -0,0 +1,7 @@
+#######
+#G..#E#
+#E#E.E#
+#G.##.#
+#...#E#
+#...E.#
+#######

2018/src/samples/15.3.txt

@@ -0,0 +1,7 @@
+#######
+#E..EG#
+#.#G.E#
+#E.##E#
+#G..#.#
+#..E#.#
+#######

2018/src/samples/15.4.txt

@@ -0,0 +1,7 @@
+#######
+#E.G#.#
+#.#G..#
+#G.#.G#
+#G..#.#
+#...E.#
+#######

2018/src/samples/15.5.txt

@@ -0,0 +1,7 @@
+#######
+#.E...#
+#.#..G#
+#.###.#
+#E#G#G#
+#...#G#
+#######

2018/src/samples/15.6.txt

@@ -0,0 +1,9 @@
+#########
+#G......#
+#.E.#...#
+#..##..G#
+#...##..#
+#...#...#
+#.G...G.#
+#.....G.#
+#########