diff --git a/2018/src/day24.rs b/2018/src/day24.rs
index 1411e52..91003e5 100644
--- a/2018/src/day24.rs
+++ b/2018/src/day24.rs
@@ -1,19 +1,193 @@
+use std::cmp::Ordering;
+use std::cmp::Reverse;
+use std::io::BufRead;
+use std::io::BufReader;
 use std::io::Read;
 
+use itertools::Itertools;
+use regex::Regex;
+
 use common::Solution;
 
+#[derive(Default, Debug, Eq, PartialEq, Clone)]
+struct Group {
+    power: u32,
+    count: u32,
+    hp: u32,
+    initiative: i32,
+    damage: String,
+    weaknesses: Vec<String>,
+    immunities: Vec<String>,
+    faction: char,
+}
+
+impl Group {
+    pub fn is_alive(&self) -> bool {
+        self.count > 0
+    }
+
+    pub fn damage_to(&self, other: &Group) -> u32 {
+        let damage = self.effective_power();
+
+        if other.weaknesses.contains(&self.damage) {
+            damage * 2
+        } else if other.immunities.contains(&self.damage) {
+            0
+        } else {
+            damage
+        }
+    }
+
+    pub fn effective_power(&self) -> u32 {
+        self.power * self.count
+    }
+}
+
+impl Ord for Group {
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.effective_power().cmp(&other.effective_power())
+            .then(other.initiative.cmp(&self.initiative))
+    }
+}
+
+impl PartialOrd for Group {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
 #[derive(Default)]
-pub struct Day24 {}
+pub struct Day24 {
+    units: Vec<Group>,
+}
 
 impl Day24 {
     pub fn new() -> Self {
         Default::default()
     }
+
+    fn read_input(&mut self, input: &mut Read) {
+        let matcher = Regex::new(r"(\d+) units each with (\d+) hit points (\(([^)]+)\) )?with an attack that does (\d+) (\w+) damage at initiative (\d+)").unwrap();
+        let weakness_matcher = Regex::new(r"(weak|immune) to ([^;)]+)").unwrap();
+        let reader = BufReader::new(input);
+        let mut fac = 'X';
+
+        for line in reader.lines() {
+            let line = line.unwrap();
+            match line.as_str() {
+                "Immune System:" => { fac = 'D' }
+                "" => {}
+                "Infection:" => { fac = 'I' }
+                line => {
+                    let caps = matcher.captures(line).unwrap_or_else(|| {
+                        panic!("{}", line);
+                    });
+
+                    let mut group = Group {
+                        count: caps[1].parse().unwrap(),
+                        hp: caps[2].parse().unwrap(),
+                        power: caps[5].parse().unwrap(),
+                        damage: caps[6].to_string(),
+                        initiative: caps[7].parse().unwrap(),
+                        faction: fac,
+                        ..Default::default()
+                    };
+
+                    if let Some(caps) = caps.get(4) {
+                        for modified in weakness_matcher.captures_iter(caps.as_str()) {
+                            let target = match &modified[1] {
+                                "weak" => &mut group.weaknesses,
+                                "immune" => &mut group.immunities,
+                                _ => panic!(),
+                            };
+
+                            for t in modified[2].split(", ") {
+                                target.push(t.to_string());
+                            }
+                        }
+                    }
+                    self.units.push(group)
+                }
+            }
+        }
+    }
+
+    fn simulate(&mut self) {
+        let mut order: Vec<usize> = (0..self.units.len()).collect();
+        order.sort_unstable_by_key(|&x| &self.units[x]);
+        order.reverse();
+
+        // select targets
+        let mut targets: Vec<Option<usize>> = vec![None; self.units.len()];
+        let mut is_targeted = vec![false; self.units.len()];
+
+        for &i in &order {
+            let unit = &self.units[i];
+            if !unit.is_alive() {
+                continue;
+            }
+            let damage = self.units.iter().map(|x| unit.damage_to(x)).collect_vec();
+            let target = (0..self.units.len())
+                .filter(|&x| !is_targeted[x] && self.units[x].faction != unit.faction)
+                .max_by(|&x, &y| {
+                    damage[x].cmp(&damage[y])
+                        .then(self.units[x].effective_power().cmp(&self.units[y].effective_power()))
+                        .then(self.units[x].initiative.cmp(&self.units[y].initiative))
+                });
+
+            if let Some(target) = target {
+                println!("{} will attack {}, dealing {}", i, target, damage[target]);
+                targets[i] = Some(target);
+                is_targeted[target] = true;
+            }
+        }
+
+        order.sort_unstable_by_key(|&x| Reverse(self.units[x].initiative));
+        println!("{:?}", order);
+
+        for attacker in order {
+            if !self.units[attacker].is_alive() {
+                continue;
+            }
+
+            if let Some(id) = targets[attacker] {
+                let damage = self.units[attacker].damage_to(&self.units[id]);
+                let defender = &mut self.units[id];
+
+                let losses = damage / defender.hp;
+                println!("{} does {} damage to {}. Killed {}", attacker, damage, id, losses);
+                defender.count = defender.count.saturating_sub(losses);
+            }
+        }
+    }
+
+    fn both_alive(&self) -> bool {
+        let mut seen = None;
+
+        for unit in self.units.iter().filter(|g| g.is_alive()) {
+            if let Some(seen) = seen {
+                if seen != unit.faction {
+                    return true;
+                }
+                continue;
+            }
+
+            seen = Some(unit.faction);
+        }
+
+        return false;
+    }
 }
 
 impl Solution for Day24 {
-    fn part1(&mut self, _input: &mut Read) -> String {
-        unimplemented!()
+    fn part1(&mut self, input: &mut Read) -> String {
+        self.read_input(input);
+        while self.both_alive() {
+            self.simulate();
+        }
+
+        let result: u32 = self.units.iter().map(|x| x.count).sum();
+        result.to_string()
     }
 
     fn part2(&mut self, _input: &mut Read) -> String {
@@ -22,4 +196,15 @@ impl Solution for Day24 {
 }
 
 #[cfg(test)]
-mod tests {}
+mod tests {
+    use common::Solution;
+    use day24::Day24;
+
+    const SAMPLE_INPUT: &[u8] = include_bytes!("samples/24.txt");
+
+    #[test]
+    fn sample_part1() {
+        let mut instance = Day24::new();
+        assert_eq!("5216", instance.part1(&mut SAMPLE_INPUT))
+    }
+}
diff --git a/2018/src/samples/24.txt b/2018/src/samples/24.txt
new file mode 100644
index 0000000..7a474c9
--- /dev/null
+++ b/2018/src/samples/24.txt
@@ -0,0 +1,7 @@
+Immune System:
+17 units each with 5390 hit points (weak to radiation, bludgeoning) with an attack that does 4507 fire damage at initiative 2
+989 units each with 1274 hit points (immune to fire; weak to bludgeoning, slashing) with an attack that does 25 slashing damage at initiative 3
+
+Infection:
+801 units each with 4706 hit points (weak to radiation) with an attack that does 116 bludgeoning damage at initiative 1
+4485 units each with 2961 hit points (immune to radiation; weak to fire, cold) with an attack that does 12 slashing damage at initiative 4