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December 2, 2018 06:59
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Advent of Code 2018, day 1
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| // prepare the puzzle input | |
| let input = loadFile(named: "day1") // convenience function in resources | |
| .split(separator: "\n") | |
| .compactMap(Int.init) // extension on Int to init? with String.Subsequence | |
| // part 1 | |
| let part1 = input.reduce(0, +) | |
| // part 2 | |
| // Make an infinite sequence from the input | |
| let frequencies = sequence(state: input.startIndex) { (index) -> Int? in | |
| defer { | |
| index = index.advanced(by: 1) | |
| } | |
| if index == input.endIndex { | |
| index = input.startIndex | |
| } | |
| return input[index] | |
| } | |
| var history = Set<Int>([0]) | |
| var current = 0 | |
| for frequency in frequencies { | |
| current += frequency | |
| if !history.contains(current) { | |
| history.insert(current) | |
| continue | |
| } | |
| break | |
| } | |
| let part2 = current |
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