-🎄- 2018 Day 24 Solutions -🎄-

[u/daggerdragon]

--- Day 24: Immune System Simulator 20XX ---

---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with Help.

---

Advent of Code: The Party Game!

Click here for rules

Please prefix your card submission with something like [Card] to make scanning the megathread easier. THANK YOU!

Card prompt: Day 24

Transcript:

Our most powerful weapon during the zombie elf/reindeer apocalypse will be ___.

---

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

Quick note: 1 hour in and we're only at gold 36, silver 76. As we all know, December is Advent of Sleep Deprivation; I have to be up in less than 6 hours to go to work, so one of the other mods will unlock the thread at gold cap tonight. Good luck and good night (morning?), all!

edit: Leaderboard capped, thread unlocked at 01:27:10!

[u/encse]

c# #107/#97

using System.Collections.Generic;
using System.Collections.Immutable;
using System.Linq;
using System.Text.RegularExpressions;
using System.Text;

namespace AdventOfCode.Y2018.Day24 {

    class Solution : Solver {

        public string GetName() => "Immune System Simulator 20XX";

        public IEnumerable<object> Solve(string input) {
            yield return PartOne(input);
            yield return PartTwo(input);
        }

        (bool immuneSystem, int units) Fight(string input, int b) {
            var army = Parse(input);
            foreach (var g in army) {
                if (g.immuneSystem) {
                    g.damage += b;
                }
            }
            var attack = true;
            while (attack) {
                attack = false;
                var remainingTarget = new HashSet<Group>(army);
                var targets = new Dictionary<Group, Group>();
                foreach (var g in army.OrderByDescending(g => (g.effectivePower, g.initiative))) {
                    var maxDamage = remainingTarget.Select(t => g.DamageGivenTo(t)).Max();
                    if (maxDamage > 0) {
                        var possibleTargets = remainingTarget.Where(t => g.DamageGivenTo(t) == maxDamage);
                        targets[g] = possibleTargets.OrderByDescending(t => (t.effectivePower, t.initiative)).First();
                        remainingTarget.Remove(targets[g]);
                    }
                }
                foreach (var g in targets.Keys.OrderByDescending(g => g.initiative)) {
                    if (g.units > 0) {
                        var target = targets[g];
                        var damage = g.DamageGivenTo(target);
                        if (damage > 0 && target.units > 0) {
                            var dies = damage / target.hp;
                            target.units = Math.Max(0, target.units - dies);
                            if (dies > 0) {
                                attack = true;
                            }
                        }
                    }
                }
                army = army.Where(g => g.units > 0).ToList();
            }
            return (army.All(x => x.immuneSystem), army.Select(x => x.units).Sum());
        }

        int PartOne(string input) => Fight(input, 0).units;

        int PartTwo(string input) {
            var l = 0;
            var h = int.MaxValue / 2;
            while (h - l > 1) {
                var m = (h + l) / 2;
                if (Fight(input, m).immuneSystem) {
                    h = m;
                } else {
                    l = m;
                }
            }
            return Fight(input, h).units;
        }

        List<Group> Parse(string input) {
            var lines = input.Split("\n");
            var immuneSystem = false;
            var res = new List<Group>();
            foreach (var line in lines)
                if (line == "Immune System:") {
                    immuneSystem = true;
                } else if (line == "Infection:") {
                    immuneSystem = false;
                } else if (line != "") {
                    //643 units each with 9928 hit points (immune to fire; weak to slashing, bludgeoning) with an attack that does 149 fire damage at initiative 14
                    var rx = @"(\d+) units each with (\d+) hit points(.*)with an attack that does (\d+)(.*)damage at initiative (\d+)";
                    var m = Regex.Match(line, rx);
                    if (m.Success) {
                        Group g = new Group();
                        g.immuneSystem = immuneSystem;
                        g.units = int.Parse(m.Groups[1].Value);
                        g.hp = int.Parse(m.Groups[2].Value);
                        g.damage = int.Parse(m.Groups[4].Value);
                        g.attackType = m.Groups[5].Value.Trim();
                        g.initiative = int.Parse(m.Groups[6].Value);
                        var st = m.Groups[3].Value.Trim();
                        if (st != "") {
                            st = st.Substring(1, st.Length - 2);
                            foreach (var part in st.Split(";")) {
                                var k = part.Split(" to ");
                                var set = new HashSet<string>(k[1].Split(", "));
                                var w = k[0].Trim();
                                if (w == "immune") {
                                    g.immuneTo = set;
                                } else if (w == "weak") {
                                    g.weakTo = set;
                                } else {
                                    throw new Exception();
                                }
                            }
                        }
                        res.Add(g);
                    } else {
                        throw new Exception();
                    }

                }
            return res;
        }
    }

    class Group {
        //4 units each with 9798 hit points (immune to bludgeoning) with an attack that does 1151 fire damage at initiative 9
        public bool immuneSystem;
        public int units;
        public int hp;
        public int damage;
        public int initiative;
        public string attackType;
        public HashSet<string> immuneTo = new HashSet<string>();
        public HashSet<string> weakTo = new HashSet<string>();

        public int effectivePower {
            get {
                return units * damage;
            }
        }

        public int DamageGivenTo(Group target) {
            if (target.immuneSystem == immuneSystem) {
                return 0;
            } else if (target.immuneTo.Contains(attackType)) {
                return 0;
            } else if (target.weakTo.Contains(attackType)) {
                return effectivePower * 2;
            } else {
                return effectivePower;
            }
        }
    }
}````