61 lines
1.1 KiB
Swift
61 lines
1.1 KiB
Swift
import Foundation
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let input = loadData(day: 13)
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let scanner = Scanner(string: input)
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let startTime = scanner.scanInt()!
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var busLines: [(Int, position: Int)] = []
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var position = 0
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repeat {
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if let line = scanner.scanInt() {
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busLines.append((line, position))
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} else if scanner.string("x") {
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// Ignore
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}
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position += 1
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} while scanner.string(",")
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let min = busLines
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.map { $0.0 }
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.map { ((startTime / $0) * $0 + $0, $0) }
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.print()
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.min(by: { $0.0 < $1.0 })!
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print((min.0 - startTime) * min.1)
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let max = busLines.max(by: { $0.0 < $1.0 })!
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print(max)
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/*
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brute force - takes too long
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var s = sequence(first: 0, next: { $0 + max.0 })
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.lazy
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.filter { t in busLines.allSatisfy { (t - max.position + $0.position).isMultiple(of: $0.0 )} }
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.makeIterator()
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print(s.next())
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*/
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var step = 0
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var time = 0
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outer: while true {
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time += step
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step = 1
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for (bus, position) in busLines {
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guard (time + position).isMultiple(of: bus) else { continue outer }
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step *= bus
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}
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break
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}
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print("part2", time)
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