56 lines
1.6 KiB
C#
56 lines
1.6 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 int[]? _initialList;
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public Day16() : base(2019, 16, "Flawed Frequency Transmission")
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{
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}
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public override void ProcessInput()
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{
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_initialList = Input.First().Select(c => c - '0').ToArray();
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}
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public override object Part1()
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{
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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 < 100; i++)
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if (i % 2 == 0)
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CalculateSignal(signal0, signal1);
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else
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CalculateSignal(signal1, signal0);
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return new string(signal0.Take(8).Select(c => (char)(c + '0')).ToArray());
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}
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public override object Part2()
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{
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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 < 100; 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 string(signal.Take(8).Select(c => (char)(c + '0')).ToArray());
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}
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private static void CalculateSignal(int[] input, int[] output)
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{
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for (var j = 0; j < output.Length; j++)
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output[j] = Math.Abs(BasePattern
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.SelectMany(v => Enumerable.Repeat(v, j + 1))
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.Repeat()
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.Skip(1)
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.Take(input.Length)
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.Select((pv, i) => pv * input[i] % 10).Sum()) % 10;
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}
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} |