75 lines
2.3 KiB
Nim
75 lines
2.3 KiB
Nim
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# Copyright 2021 Christian Ulrich
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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# usage: ./part2 < input
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import bitops
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import sequtils
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proc readNumbers(): tuple[numbers: seq[uint64], numberWidth: int] =
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var
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line = ""
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while readLine(stdin, line):
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if line.len() > 0:
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if line.len() != result.numberWidth:
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if result.numberWidth == 0:
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result.numberWidth = line.len()
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else:
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raise newException(ValueError, "invalid line length")
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var number = 0'u64
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for index, digit in line.pairs():
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case digit
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of '0': discard
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of '1': number.setBit(result.numberWidth - 1 - index)
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else: raise newException(ValueError, "invalid number")
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result.numbers.add(number)
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proc countBits(numbers: seq[uint64], bitPos: int): tuple[ones: int, zeros: int] =
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for number in numbers:
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if number.testBit(bitPos):
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result.ones.inc()
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else:
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result.zeros.inc()
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proc findNumber(numbers: seq[uint64], numberWidth: int, mostCommon: bool): uint64 =
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var remaining = numbers
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for bitPos in countdown(numberWidth - 1, 0):
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let (ones, zeros) = remaining.countBits(bitPos)
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let required = if ones >= zeros:
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mostCommon
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else:
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not mostCommon
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remaining = remaining.filterIt(it.testBit(bitPos) == required)
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if remaining.len() == 1:
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return remaining[0]
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raise newException(ValueError, "cannot find number")
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proc lifeSupportRating(): uint64 =
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let
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(numbers, numberWidth) = readNumbers()
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oxygen = findNumber(numbers, numberWidth, true)
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co2 = findNumber(numbers, numberWidth, false)
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result = oxygen * co2
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proc main(): int =
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try:
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echo lifeSupportRating()
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except Exception as error:
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echo error.msg
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result = -1
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when isMainModule:
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quit(main())
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