2019-11-08 03:30:41 +00:00
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Advent of Code
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--- Day 24: Immune System Simulator 20XX ---
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After a weird buzzing noise, you appear back at the man's cottage. He seems
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relieved to see his friend, but quickly notices that the little reindeer
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caught some kind of cold while out exploring.
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The portly man explains that this reindeer's immune system isn't similar to
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regular reindeer immune systems:
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The immune system and the infection each have an army made up of several
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groups; each group consists of one or more identical units. The armies
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repeatedly fight until only one army has units remaining.
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Units within a group all have the same hit points (amount of damage a unit
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can take before it is destroyed), attack damage (the amount of damage each
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unit deals), an attack type, an initiative (higher initiative units attack
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first and win ties), and sometimes weaknesses or immunities. Here is an
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example group:
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18 units each with 729 hit points (weak to fire; immune to cold, slashing)
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with an attack that does 8 radiation damage at initiative 10
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Each group also has an effective power: the number of units in that group
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multiplied by their attack damage. The above group has an effective power of
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18 * 8 = 144. Groups never have zero or negative units; instead, the group
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is removed from combat.
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Each fight consists of two phases: target selection and attacking.
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During the target selection phase, each group attempts to choose one target.
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In decreasing order of effective power, groups choose their targets; in a
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tie, the group with the higher initiative chooses first. The attacking group
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chooses to target the group in the enemy army to which it would deal the
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most damage (after accounting for weaknesses and immunities, but not
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accounting for whether the defending group has enough units to actually
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receive all of that damage).
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If an attacking group is considering two defending groups to which it would
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deal equal damage, it chooses to target the defending group with the largest
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effective power; if there is still a tie, it chooses the defending group
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with the highest initiative. If it cannot deal any defending groups damage,
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it does not choose a target. Defending groups can only be chosen as a target
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by one attacking group.
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At the end of the target selection phase, each group has selected zero or
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one groups to attack, and each group is being attacked by zero or one
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groups.
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During the attacking phase, each group deals damage to the target it
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selected, if any. Groups attack in decreasing order of initiative,
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regardless of whether they are part of the infection or the immune system.
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(If a group contains no units, it cannot attack.)
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The damage an attacking group deals to a defending group depends on the
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attacking group's attack type and the defending group's immunities and
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weaknesses. By default, an attacking group would deal damage equal to its
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effective power to the defending group. However, if the defending group is
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immune to the attacking group's attack type, the defending group instead
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takes no damage; if the defending group is weak to the attacking group's
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attack type, the defending group instead takes double damage.
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The defending group only loses whole units from damage; damage is always
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dealt in such a way that it kills the most units possible, and any remaining
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damage to a unit that does not immediately kill it is ignored. For example,
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if a defending group contains 10 units with 10 hit points each and receives
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75 damage, it loses exactly 7 units and is left with 3 units at full health.
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After the fight is over, if both armies still contain units, a new fight
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begins; combat only ends once one army has lost all of its units.
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For example, consider the following armies:
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2019-11-08 18:40:42 +00:00
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Immune System: 17 units each with 5390 hit points (weak to radiation,
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bludgeoning) with an attack that does 4507 fire damage at initiative 2 989
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units each with 1274 hit points (immune to fire; weak to bludgeoning,
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slashing) with an attack that does 25 slashing damage at initiative 3
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Infection: 801 units each with 4706 hit points (weak to radiation) with an
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attack that does 116 bludgeoning damage at initiative 1 4485 units each with
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2961 hit points (immune to radiation; weak to fire, cold) with an attack that
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does 12 slashing damage at initiative 4
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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If these armies were to enter combat, the following fights, including
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details during the target selection and attacking phases, would take place:
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Immune System: Group 1 contains 17 units Group 2 contains 989 units Infection:
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Group 1 contains 801 units Group 2 contains 4485 units
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Infection group 1 would deal defending group 1 185832 damage Infection group 1
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would deal defending group 2 185832 damage Infection group 2 would deal
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defending group 2 107640 damage Immune System group 1 would deal defending
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group 1 76619 damage Immune System group 1 would deal defending group 2 153238
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damage Immune System group 2 would deal defending group 1 24725 damage
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Infection group 2 attacks defending group 2, killing 84 units Immune System
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group 2 attacks defending group 1, killing 4 units Immune System group 1
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attacks defending group 2, killing 51 units Infection group 1 attacks
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defending group 1, killing 17 units
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Immune System: Group 2 contains 905 units Infection: Group 1 contains 797
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units Group 2 contains 4434 units
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Infection group 1 would deal defending group 2 184904 damage Immune System
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group 2 would deal defending group 1 22625 damage Immune System group 2 would
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deal defending group 2 22625 damage
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Immune System group 2 attacks defending group 1, killing 4 units Infection
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group 1 attacks defending group 2, killing 144 units
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Immune System: Group 2 contains 761 units Infection: Group 1 contains 793
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units Group 2 contains 4434 units
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Infection group 1 would deal defending group 2 183976 damage Immune System
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group 2 would deal defending group 1 19025 damage Immune System group 2 would
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deal defending group 2 19025 damage
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Immune System group 2 attacks defending group 1, killing 4 units Infection
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group 1 attacks defending group 2, killing 143 units
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2019-11-08 18:40:42 +00:00
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Immune System: Group 2 contains 618 units Infection: Group 1 contains 789
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units Group 2 contains 4434 units
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Infection group 1 would deal defending group 2 183048 damage Immune System
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group 2 would deal defending group 1 15450 damage Immune System group 2 would
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deal defending group 2 15450 damage
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Immune System group 2 attacks defending group 1, killing 3 units Infection
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group 1 attacks defending group 2, killing 143 units
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Immune System: Group 2 contains 475 units Infection: Group 1 contains 786
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units Group 2 contains 4434 units
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Infection group 1 would deal defending group 2 182352 damage Immune System
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group 2 would deal defending group 1 11875 damage Immune System group 2 would
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deal defending group 2 11875 damage
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Immune System group 2 attacks defending group 1, killing 2 units Infection
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group 1 attacks defending group 2, killing 142 units
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Immune System: Group 2 contains 333 units Infection: Group 1 contains 784
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units Group 2 contains 4434 units
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2019-11-08 18:40:42 +00:00
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Infection group 1 would deal defending group 2 181888 damage Immune System
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group 2 would deal defending group 1 8325 damage Immune System group 2 would
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deal defending group 2 8325 damage
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Immune System group 2 attacks defending group 1, killing 1 unit Infection
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group 1 attacks defending group 2, killing 142 units
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Immune System: Group 2 contains 191 units Infection: Group 1 contains 783
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units Group 2 contains 4434 units
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Infection group 1 would deal defending group 2 181656 damage Immune System
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group 2 would deal defending group 1 4775 damage Immune System group 2 would
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deal defending group 2 4775 damage
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Immune System group 2 attacks defending group 1, killing 1 unit Infection
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group 1 attacks defending group 2, killing 142 units
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Immune System: Group 2 contains 49 units Infection: Group 1 contains 782 units
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2019-11-08 03:30:41 +00:00
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Group 2 contains 4434 units
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2019-11-08 18:40:42 +00:00
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Infection group 1 would deal defending group 2 181424 damage Immune System
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group 2 would deal defending group 1 1225 damage Immune System group 2 would
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deal defending group 2 1225 damage
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Immune System group 2 attacks defending group 1, killing 0 units Infection
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group 1 attacks defending group 2, killing 49 units
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Immune System: No groups remain. Infection: Group 1 contains 782 units Group 2
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contains 4434 units
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2019-11-08 03:30:41 +00:00
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In the example above, the winning army ends up with 782 + 4434 = 5216 units.
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2019-11-08 18:40:42 +00:00
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You scan the reindeer's condition (your puzzle input); the white-bearded man
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looks nervous. As it stands now, how many units would the winning army have?
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Your puzzle answer was 16747.
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--- Part Two ---
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Things aren't looking good for the reindeer. The man asks whether more milk
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and cookies would help you think.
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If only you could give the reindeer's immune system a boost, you might be
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able to change the outcome of the combat.
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A boost is an integer increase in immune system units' attack damage. For
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example, if you were to boost the above example's immune system's units by
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1570, the armies would instead look like this:
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Immune System: 17 units each with 5390 hit points (weak to radiation,
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bludgeoning) with an attack that does 6077 fire damage at initiative 2 989
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units each with 1274 hit points (immune to fire; weak to bludgeoning,
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slashing) with an attack that does 1595 slashing damage at initiative 3
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Infection: 801 units each with 4706 hit points (weak to radiation) with an
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attack that does 116 bludgeoning damage at initiative 1 4485 units each with
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2961 hit points (immune to radiation; weak to fire, cold) with an attack that
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does 12 slashing damage at initiative 4
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With this boost, the combat proceeds differently:
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Immune System: Group 2 contains 989 units Group 1 contains 17 units Infection:
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Group 1 contains 801 units Group 2 contains 4485 units
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Infection group 1 would deal defending group 2 185832 damage Infection group 1
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would deal defending group 1 185832 damage Infection group 2 would deal
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defending group 1 53820 damage Immune System group 2 would deal defending
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group 1 1577455 damage Immune System group 2 would deal defending group 2
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1577455 damage Immune System group 1 would deal defending group 2 206618
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damage
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Infection group 2 attacks defending group 1, killing 9 units Immune System
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group 2 attacks defending group 1, killing 335 units Immune System group 1
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attacks defending group 2, killing 32 units Infection group 1 attacks
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defending group 2, killing 84 units
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Immune System: Group 2 contains 905 units Group 1 contains 8 units Infection:
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Group 1 contains 466 units Group 2 contains 4453 units
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Infection group 1 would deal defending group 2 108112 damage Infection group 1
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would deal defending group 1 108112 damage Infection group 2 would deal
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defending group 1 53436 damage Immune System group 2 would deal defending
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group 1 1443475 damage Immune System group 2 would deal defending group 2
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1443475 damage Immune System group 1 would deal defending group 2 97232 damage
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Infection group 2 attacks defending group 1, killing 8 units Immune System
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group 2 attacks defending group 1, killing 306 units Infection group 1 attacks
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defending group 2, killing 29 units
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Immune System: Group 2 contains 876 units Infection: Group 2 contains 4453
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units Group 1 contains 160 units
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2019-11-08 03:30:41 +00:00
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2019-11-08 18:40:42 +00:00
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Infection group 2 would deal defending group 2 106872 damage Immune System
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group 2 would deal defending group 2 1397220 damage Immune System group 2
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would deal defending group 1 1397220 damage
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Infection group 2 attacks defending group 2, killing 83 units Immune System
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group 2 attacks defending group 2, killing 427 units
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After a few fights...
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Immune System: Group 2 contains 64 units Infection: Group 2 contains 214 units
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Group 1 contains 19 units
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Infection group 2 would deal defending group 2 5136 damage Immune System group
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2 would deal defending group 2 102080 damage Immune System group 2 would deal
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defending group 1 102080 damage
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Infection group 2 attacks defending group 2, killing 4 units Immune System
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group 2 attacks defending group 2, killing 32 units
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Immune System: Group 2 contains 60 units Infection: Group 1 contains 19 units
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Group 2 contains 182 units
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Infection group 1 would deal defending group 2 4408 damage Immune System group
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2 would deal defending group 1 95700 damage Immune System group 2 would deal
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defending group 2 95700 damage
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Immune System group 2 attacks defending group 1, killing 19 units
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Immune System: Group 2 contains 60 units Infection: Group 2 contains 182 units
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Infection group 2 would deal defending group 2 4368 damage Immune System group
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2 would deal defending group 2 95700 damage
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Infection group 2 attacks defending group 2, killing 3 units Immune System
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group 2 attacks defending group 2, killing 30 units
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After a few more fights...
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Immune System: Group 2 contains 51 units Infection: Group 2 contains 40 units
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Infection group 2 would deal defending group 2 960 damage Immune System group
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2 would deal defending group 2 81345 damage
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Infection group 2 attacks defending group 2, killing 0 units Immune System
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group 2 attacks defending group 2, killing 27 units
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Immune System: Group 2 contains 51 units Infection: Group 2 contains 13 units
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Infection group 2 would deal defending group 2 312 damage Immune System group
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2 would deal defending group 2 81345 damage
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Infection group 2 attacks defending group 2, killing 0 units Immune System
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group 2 attacks defending group 2, killing 13 units
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Immune System: Group 2 contains 51 units Infection: No groups remain.
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This boost would allow the immune system's armies to win! It would be left
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with 51 units.
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You don't even know how you could boost the reindeer's immune system or what
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effect it might have, so you need to be cautious and find the smallest boost
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that would allow the immune system to win.
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How many units does the immune system have left after getting the smallest
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boost it needs to win?
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Your puzzle answer was 5923.
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Both parts of this puzzle are complete! They provide two gold stars: **
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At this point, you should return to your Advent calendar and try another
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puzzle.
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If you still want to see it, you can get your puzzle input.
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2019-11-08 03:30:41 +00:00
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References
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Visible links
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. https://adventofcode.com/
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. https://adventofcode.com/2018/about
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. https://adventofcode.com/2018/events
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. https://adventofcode.com/2018/settings
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. https://adventofcode.com/2018/auth/logout
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. Advent of Code Supporter
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https://adventofcode.com/2018/support
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. https://adventofcode.com/2018
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. https://adventofcode.com/2018
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. https://adventofcode.com/2018/support
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. https://adventofcode.com/2018/sponsors
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. https://adventofcode.com/2018/leaderboard
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. https://adventofcode.com/2018/stats
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. https://adventofcode.com/2018/sponsors
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. https://www.youtube.com/watch?v=NDVjLt_QHL8&t=7
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2019-11-08 18:40:42 +00:00
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. https://adventofcode.com/2018
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2019-11-08 03:30:41 +00:00
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. https://adventofcode.com/2018/day/24/input
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