Init Day 24 directory

2018/24/README.md

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+# Answers
+
+|  Part 1  |  Part 2  |
+|----------|----------|
+| `614812` | `212176` |
+
+## --- Day 24: Immune System Simulator 20XX ---
+
+After [a weird buzzing noise](https://www.youtube.com/watch?v=NDVjLt_QHL8&t=7), you appear back at the man's cottage. He seems relieved to see his friend, but quickly notices that the little reindeer caught some kind of cold while out exploring.
+
+The portly man explains that this reindeer's immune system isn't similar to regular reindeer immune systems:
+
+The _immune system_ and the _infection_ each have an army made up of several _groups_; each _group_ consists of one or more identical _units_. The armies repeatedly _fight_ until only one army has units remaining.
+
+_Units_ within a group all have the same _hit points_ (amount of damage a unit can take before it is destroyed), _attack damage_ (the amount of damage each unit deals), an _attack type_, an _initiative_ (higher initiative units attack first and win ties), and sometimes _weaknesses_ or _immunities_. Here is an example group:
+
+    18 units each with 729 hit points (weak to fire; immune to cold, slashing)
+     with an attack that does 8 radiation damage at initiative 10
+
+
+Each group also has an _effective power_: the number of units in that group multiplied by their attack damage. The above group has an effective power of `18 * 8 = 144`. Groups never have zero or negative units; instead, the group is removed from combat.
+
+Each _fight_ consists of two phases: _target selection_ and _attacking_.
+
+During the _target selection_ phase, each group attempts to choose one target. In decreasing order of effective power, groups choose their targets; in a tie, the group with the higher initiative chooses first. The attacking group chooses to target the group in the enemy army to which it would deal the most damage (after accounting for weaknesses and immunities, but not accounting for whether the defending group has enough units to actually receive all of that damage).
+
+If an attacking group is considering two defending groups to which it would deal equal damage, it chooses to target the defending group with the largest effective power; if there is still a tie, it chooses the defending group with the highest initiative. If it cannot deal any defending groups damage, it does not choose a target. Defending groups can only be chosen as a target by one attacking group.
+
+At the end of the target selection phase, each group has selected zero or one groups to attack, and each group is being attacked by zero or one groups.
+
+During the _attacking_ phase, each group deals damage to the target it selected, if any. Groups attack in decreasing order of initiative, regardless of whether they are part of the infection or the immune system. (If a group contains no units, it cannot attack.)
+
+The damage an attacking group deals to a defending group depends on the attacking group's attack type and the defending group's immunities and weaknesses. By default, an attacking group would deal damage equal to its _effective power_ to the defending group. However, if the defending group is _immune_ to the attacking group's attack type, the defending group instead takes _no damage_; if the defending group is _weak_ to the attacking group's attack type, the defending group instead takes _double damage_.
+
+The defending group only loses _whole units_ from damage; damage is always dealt in such a way that it kills the most units possible, and any remaining damage to a unit that does not immediately kill it is ignored. For example, if a defending group contains `10` units with `10` hit points each and receives `75` damage, it loses exactly `7` units and is left with `3` units at full health.
+
+After the fight is over, if both armies still contain units, a new fight begins; combat only ends once one army has lost all of its units.
+
+For example, consider the following armies:
+
+    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
+
+
+If these armies were to enter combat, the following fights, including details during the target selection and attacking phases, would take place:
+
+    Immune System:
+    Group 1 contains 17 units
+    Group 2 contains 989 units
+    Infection:
+    Group 1 contains 801 units
+    Group 2 contains 4485 units
+
+    Infection group 1 would deal defending group 1 185832 damage
+    Infection group 1 would deal defending group 2 185832 damage
+    Infection group 2 would deal defending group 2 107640 damage
+    Immune System group 1 would deal defending group 1 76619 damage
+    Immune System group 1 would deal defending group 2 153238 damage
+    Immune System group 2 would deal defending group 1 24725 damage
+
+    Infection group 2 attacks defending group 2, killing 84 units
+    Immune System group 2 attacks defending group 1, killing 4 units
+    Immune System group 1 attacks defending group 2, killing 51 units
+    Infection group 1 attacks defending group 1, killing 17 units
+
+
+    Immune System:
+    Group 2 contains 905 units
+    Infection:
+    Group 1 contains 797 units
+    Group 2 contains 4434 units
+
+    Infection group 1 would deal defending group 2 184904 damage
+    Immune System group 2 would deal defending group 1 22625 damage
+    Immune System group 2 would deal defending group 2 22625 damage
+
+    Immune System group 2 attacks defending group 1, killing 4 units
+    Infection group 1 attacks defending group 2, killing 144 units
+
+
+    Immune System:
+    Group 2 contains 761 units
+    Infection:
+    Group 1 contains 793 units
+    Group 2 contains 4434 units
+
+    Infection group 1 would deal defending group 2 183976 damage
+    Immune System group 2 would deal defending group 1 19025 damage
+    Immune System group 2 would deal defending group 2 19025 damage
+
+    Immune System group 2 attacks defending group 1, killing 4 units
+    Infection group 1 attacks defending group 2, killing 143 units
+
+
+    Immune System:
+    Group 2 contains 618 units
+    Infection:
+    Group 1 contains 789 units
+    Group 2 contains 4434 units
+
+    Infection group 1 would deal defending group 2 183048 damage
+    Immune System group 2 would deal defending group 1 15450 damage
+    Immune System group 2 would deal defending group 2 15450 damage
+
+    Immune System group 2 attacks defending group 1, killing 3 units
+    Infection group 1 attacks defending group 2, killing 143 units
+
+
+    Immune System:
+    Group 2 contains 475 units
+    Infection:
+    Group 1 contains 786 units
+    Group 2 contains 4434 units
+
+    Infection group 1 would deal defending group 2 182352 damage
+    Immune System group 2 would deal defending group 1 11875 damage
+    Immune System group 2 would deal defending group 2 11875 damage
+
+    Immune System group 2 attacks defending group 1, killing 2 units
+    Infection group 1 attacks defending group 2, killing 142 units
+
+
+    Immune System:
+    Group 2 contains 333 units
+    Infection:
+    Group 1 contains 784 units
+    Group 2 contains 4434 units
+
+    Infection group 1 would deal defending group 2 181888 damage
+    Immune System group 2 would deal defending group 1 8325 damage
+    Immune System group 2 would deal defending group 2 8325 damage
+
+    Immune System group 2 attacks defending group 1, killing 1 unit
+    Infection group 1 attacks defending group 2, killing 142 units
+
+
+    Immune System:
+    Group 2 contains 191 units
+    Infection:
+    Group 1 contains 783 units
+    Group 2 contains 4434 units
+
+    Infection group 1 would deal defending group 2 181656 damage
+    Immune System group 2 would deal defending group 1 4775 damage
+    Immune System group 2 would deal defending group 2 4775 damage
+
+    Immune System group 2 attacks defending group 1, killing 1 unit
+    Infection group 1 attacks defending group 2, killing 142 units
+
+
+    Immune System:
+    Group 2 contains 49 units
+    Infection:
+    Group 1 contains 782 units
+    Group 2 contains 4434 units
+
+    Infection group 1 would deal defending group 2 181424 damage
+    Immune System group 2 would deal defending group 1 1225 damage
+    Immune System group 2 would deal defending group 2 1225 damage
+
+    Immune System group 2 attacks defending group 1, killing 0 units
+    Infection group 1 attacks defending group 2, killing 49 units
+
+
+    Immune System:
+    No groups remain.
+    Infection:
+    Group 1 contains 782 units
+    Group 2 contains 4434 units
+
+
+In the example above, the winning army ends up with `782 + 4434 = _5216_` units.
+
+You scan the reindeer's condition (your puzzle input); the white-bearded man looks nervous. As it stands now, _how many units would the winning army have_?
+
+-----------------
+
+## --- Part Two ---
+
+Things aren't looking good for the reindeer. The man asks whether more milk and cookies would help you think.
+
+If only you could give the reindeer's immune system a boost, you might be able to change the outcome of the combat.
+
+A _boost_ is an integer increase in immune system units' attack damage. For example, if you were to boost the above example's immune system's units by `1570`, the armies would instead look like this:
+
+    Immune System:
+    17 units each with 5390 hit points (weak to radiation, bludgeoning) with
+     an attack that does 6077 fire damage at initiative 2
+    989 units each with 1274 hit points (immune to fire; weak to bludgeoning,
+     slashing) with an attack that does 1595 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
+
+
+With this boost, the combat proceeds differently:
+
+    Immune System:
+    Group 2 contains 989 units
+    Group 1 contains 17 units
+    Infection:
+    Group 1 contains 801 units
+    Group 2 contains 4485 units
+
+    Infection group 1 would deal defending group 2 185832 damage
+    Infection group 1 would deal defending group 1 185832 damage
+    Infection group 2 would deal defending group 1 53820 damage
+    Immune System group 2 would deal defending group 1 1577455 damage
+    Immune System group 2 would deal defending group 2 1577455 damage
+    Immune System group 1 would deal defending group 2 206618 damage
+
+    Infection group 2 attacks defending group 1, killing 9 units
+    Immune System group 2 attacks defending group 1, killing 335 units
+    Immune System group 1 attacks defending group 2, killing 32 units
+    Infection group 1 attacks defending group 2, killing 84 units
+
+
+    Immune System:
+    Group 2 contains 905 units
+    Group 1 contains 8 units
+    Infection:
+    Group 1 contains 466 units
+    Group 2 contains 4453 units
+
+    Infection group 1 would deal defending group 2 108112 damage
+    Infection group 1 would deal defending group 1 108112 damage
+    Infection group 2 would deal defending group 1 53436 damage
+    Immune System group 2 would deal defending group 1 1443475 damage
+    Immune System group 2 would deal defending group 2 1443475 damage
+    Immune System group 1 would deal defending group 2 97232 damage
+
+    Infection group 2 attacks defending group 1, killing 8 units
+    Immune System group 2 attacks defending group 1, killing 306 units
+    Infection group 1 attacks defending group 2, killing 29 units
+
+
+    Immune System:
+    Group 2 contains 876 units
+    Infection:
+    Group 2 contains 4453 units
+    Group 1 contains 160 units
+
+    Infection group 2 would deal defending group 2 106872 damage
+    Immune System group 2 would deal defending group 2 1397220 damage
+    Immune System group 2 would deal defending group 1 1397220 damage
+
+    Infection group 2 attacks defending group 2, killing 83 units
+    Immune System group 2 attacks defending group 2, killing 427 units
+
+
+After a few fights...
+
+    Immune System:
+    Group 2 contains 64 units
+    Infection:
+    Group 2 contains 214 units
+    Group 1 contains 19 units
+
+    Infection group 2 would deal defending group 2 5136 damage
+    Immune System group 2 would deal defending group 2 102080 damage
+    Immune System group 2 would deal defending group 1 102080 damage
+
+    Infection group 2 attacks defending group 2, killing 4 units
+    Immune System group 2 attacks defending group 2, killing 32 units
+
+
+    Immune System:
+    Group 2 contains 60 units
+    Infection:
+    Group 1 contains 19 units
+    Group 2 contains 182 units
+
+    Infection group 1 would deal defending group 2 4408 damage
+    Immune System group 2 would deal defending group 1 95700 damage
+    Immune System group 2 would deal defending group 2 95700 damage
+
+    Immune System group 2 attacks defending group 1, killing 19 units
+
+
+    Immune System:
+    Group 2 contains 60 units
+    Infection:
+    Group 2 contains 182 units
+
+    Infection group 2 would deal defending group 2 4368 damage
+    Immune System group 2 would deal defending group 2 95700 damage
+
+    Infection group 2 attacks defending group 2, killing 3 units
+    Immune System group 2 attacks defending group 2, killing 30 units
+
+
+After a few more fights...
+
+    Immune System:
+    Group 2 contains 51 units
+    Infection:
+    Group 2 contains 40 units
+
+    Infection group 2 would deal defending group 2 960 damage
+    Immune System group 2 would deal defending group 2 81345 damage
+
+    Infection group 2 attacks defending group 2, killing 0 units
+    Immune System group 2 attacks defending group 2, killing 27 units
+
+
+    Immune System:
+    Group 2 contains 51 units
+    Infection:
+    Group 2 contains 13 units
+
+    Infection group 2 would deal defending group 2 312 damage
+    Immune System group 2 would deal defending group 2 81345 damage
+
+    Infection group 2 attacks defending group 2, killing 0 units
+    Immune System group 2 attacks defending group 2, killing 13 units
+
+
+    Immune System:
+    Group 2 contains 51 units
+    Infection:
+    No groups remain.
+
+
+This boost would allow the immune system's armies to win! It would be left with _`51`_ units.
+
+You don't even know _how_ you could boost the reindeer's immune system or what effect it might have, so you need to be cautious and find the _smallest boost_ that would allow the immune system to win.
+
+_How many units does the immune system have left_ after getting the smallest boost it needs to win?

2018/24/input.txt

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+Immune System:
+9936 units each with 1739 hit points (weak to slashing, fire) with an attack that does 1 slashing damage at initiative 11
+2990 units each with 9609 hit points (weak to radiation; immune to fire, cold) with an attack that does 31 cold damage at initiative 1
+2637 units each with 9485 hit points (immune to cold, slashing; weak to bludgeoning) with an attack that does 26 radiation damage at initiative 13
+1793 units each with 2680 hit points (weak to bludgeoning; immune to cold) with an attack that does 13 bludgeoning damage at initiative 10
+8222 units each with 6619 hit points (immune to fire, slashing) with an attack that does 6 bludgeoning damage at initiative 12
+550 units each with 5068 hit points with an attack that does 87 radiation damage at initiative 19
+950 units each with 8681 hit points (weak to radiation) with an attack that does 73 slashing damage at initiative 17
+28 units each with 9835 hit points with an attack that does 2979 bludgeoning damage at initiative 3
+3799 units each with 2933 hit points with an attack that does 7 slashing damage at initiative 16
+35 units each with 8999 hit points (weak to bludgeoning; immune to radiation) with an attack that does 2505 cold damage at initiative 6
+
+Infection:
+1639 units each with 28720 hit points with an attack that does 27 cold damage at initiative 8
+4968 units each with 16609 hit points (immune to slashing, bludgeoning, radiation) with an attack that does 6 fire damage at initiative 2
+3148 units each with 48970 hit points (weak to fire, bludgeoning) with an attack that does 29 slashing damage at initiative 20
+1706 units each with 30069 hit points (immune to cold, bludgeoning) with an attack that does 29 fire damage at initiative 7
+496 units each with 39909 hit points (immune to cold; weak to radiation) with an attack that does 133 bludgeoning damage at initiative 4
+358 units each with 17475 hit points with an attack that does 82 bludgeoning damage at initiative 5
+120 units each with 53629 hit points with an attack that does 807 fire damage at initiative 15
+402 units each with 44102 hit points (weak to slashing) with an attack that does 185 bludgeoning damage at initiative 14
+468 units each with 11284 hit points (weak to fire) with an attack that does 43 radiation damage at initiative 18
+4090 units each with 23075 hit points (immune to radiation) with an attack that does 10 bludgeoning damage at initiative 9