36 lines
1.1 KiB
Swift
36 lines
1.1 KiB
Swift
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let input = loadData(day: 5).lines()
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func decode(_ s: Substring, lower: Character, upper: Character, range: Range<Int>) -> (Int, Substring)
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{
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var range = range
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var start = s.startIndex
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while start != s.endIndex && (s[start] == lower || s[start] == upper) {
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let mid = (range.lowerBound + range.upperBound) / 2
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if s[start] == lower {
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range = range.lowerBound..<mid
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} else if s[start] == upper {
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range = mid..<range.upperBound
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}
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start = s.index(after: start)
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}
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return (range.lowerBound, s[start...])
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}
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func decodeSeat(_ s: String) -> Int {
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let (row, rest) = decode(s[...], lower: "F", upper: "B", range: 0..<128)
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let (column, _) = decode(rest, lower: "L", upper: "R", range: 0..<8)
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let id = row * 8 + column
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print(s, row, column, id)
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return id
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}
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let foundSeats = Set(input.map { decodeSeat($0) })
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print("max seat id", foundSeats.max() ?? -1)
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let allSeats = Set(0...(7+127*8))
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let freeSeats = allSeats.subtracting(foundSeats)
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let yours = freeSeats.first(where: { foundSeats.contains($0 + 1) && foundSeats.contains($0 - 1)})
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print("yours", yours ?? -1)
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