31 lines
852 B
Nim
31 lines
852 B
Nim
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import sets, streams, strutils, options
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# Day 1
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let day1TargetSum = 2020
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proc part1*(strm: Stream): Option[int] =
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var targets = initHashSet[int]()
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for line in strm.lines():
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let n = parseInt line
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if targets.contains(day1TargetSum - n):
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return some((day1TargetSum - n) * n)
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else:
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targets.incl n
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proc part2*(strm: Stream): Option[int] =
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# this works exactly the same as the previous algorithm, except we simply
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# permute once more
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# TODO: if I was really cool, I could split the shared functionality into
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# a shared proc
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var nums: seq[int]
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for line in strm.lines():
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nums.add parseInt line
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for n in nums:
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var iset = initHashSet[int]()
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let nTargetSum = day1TargetSum - n
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for n2 in nums:
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if iset.contains(nTargetSum - n2):
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return some(n * n2 * (nTargetSum - n2))
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iset.incl n2
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