46 lines
1.5 KiB
Nim
46 lines
1.5 KiB
Nim
import std/[strutils, sequtils, tables, strformat]
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import ./common
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const DEFAULT_DAYS = 80
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const CYCLE_DAYS = 7
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const MATURING_DAYS = 2
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proc lanternFish(input: string, days = DEFAULT_DAYS): int =
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# a place to put newly-spawned fish that are not mature enough themselves to
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# spawn within the cycle
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var maturingFish: seq[(int, int)]
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# here we will keep the counts of fish that spawn on a given day in the cycle
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var fish = newSeq[int](CYCLE_DAYS)
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# initialize our current fish counts based on the input
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for i in input.split(',').mapIt(it.parseInt()): inc fish[i]
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for day in 0..days:
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let cycleDay = day mod CYCLE_DAYS
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# since we're just about to decrement the days for all maturing fish, add
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# 1 to offset and spawn our maturing fish
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maturingFish.add((MATURING_DAYS+1, fish[cycleDay]))
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# age maturing fish
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for v in maturingFish.mitems(): dec v[0]
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# if our oldest maturing fish have now matured move them to their place in
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# the cycle
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if maturingFish[0][0] == 0:
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fish[cycleDay] += maturingFish[0][1]
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maturingFish.delete(0)
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# sum all fish counts plus the fish that were spawned two days ago
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fish.foldl(a + b) + (if maturingFish[0][0] <= 1: maturingFish[0][1] else: 0)
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let input = 6.loadInputText()
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time("day 6 part 1"): echo input.lanternFish()
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time("day 6 part 2"): echo input.lanternFish(256)
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when not defined(release):
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let testInput = "3,4,3,1,2"
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doAssert testInput.lanternFish(18) == 26
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doAssert testInput.lanternFish() == 5934
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doAssert testInput.lanternFish(256) == 26984457539
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