59 lines
1.8 KiB
C#
59 lines
1.8 KiB
C#
namespace aoc2019;
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public sealed class Day16 : Day
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{
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private static readonly int[] BasePattern = { 0, 1, 0, -1 };
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private readonly int[] initialList;
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public Day16() : base(16, "Flawed Frequency Transmission")
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{
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initialList = Input.First().Select(c => int.Parse($"{c}")).ToArray();
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}
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public override string Part1()
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{
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const int phaseCount = 100;
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var signal0 = initialList.ToArray();
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var signal1 = new int[signal0.Length];
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for (var i = 0; i < phaseCount; i++)
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CalculateSignal(i % 2 == 0 ? signal0 : signal1, i % 2 == 0 ? signal1 : signal0);
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return new(
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signal0.Take(8).Select(c => (char)(c + '0'))
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.ToArray());
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}
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public override string Part2()
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{
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const int phaseCount = 100;
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var messageOffset = initialList.Take(7).Aggregate((n, i) => n * 10 + i);
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var signal = initialList.Repeat(10_000).Skip(messageOffset).ToArray();
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for (var p = 0; p < phaseCount; p++)
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{
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signal[^1] %= 10;
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for (var i = signal.Length - 2; i >= 0; i--)
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signal[i] = (signal[i + 1] + signal[i]) % 10;
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}
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return new(signal.Take(8).Select(c => (char)(c + '0')).ToArray());
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}
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private static void CalculateSignal(IReadOnlyList<int> input, IList<int> output)
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{
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for (var outputIndex = 0; outputIndex < output.Count; outputIndex++)
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output[outputIndex] =
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Math.Abs(PatternValues(outputIndex, input.Count).Select((pv, i) => pv * input[i] % 10).Sum()) % 10;
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}
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private static IEnumerable<int> PatternValues(int index, int count)
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{
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return BasePattern
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.SelectMany(v => Enumerable.Repeat(v, index + 1))
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.Repeat(int.MaxValue)
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.Skip(1)
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.Take(count);
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}
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}
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