61 lines
1.6 KiB
C#
61 lines
1.6 KiB
C#
namespace AOC2021;
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/// <summary>
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/// Day 3: <a href="https://adventofcode.com/2021/day/3"/>
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/// </summary>
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public sealed class Day03() : Day(2021, 3, "Binary Diagnostic")
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{
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private List<string>? _report;
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public override void ProcessInput() =>
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_report = Input.ToList();
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public override object Part1()
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{
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var l = _report!.Count / 2;
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var g = new StringBuilder();
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var e = new StringBuilder();
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foreach (var i in Enumerable.Range(0, _report[0].Length))
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{
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var ones = _report.Select(r => r[i]).Count(c => c == '1');
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g.Append(ones > l ? '1' : '0');
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e.Append(ones > l ? '0' : '1');
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}
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var gamma = g.ToString().BigIntegerFromBinaryString();
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var epsilon = e.ToString().BigIntegerFromBinaryString();
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return gamma * epsilon;
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}
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public override object Part2()
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{
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var o = _report!;
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var c = _report!;
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var i = 0;
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while (o.Count > 1)
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{
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var most = MostCommon(i, o);
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o = o.Where(r => r[i] == most).ToList();
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i++;
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}
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var o2 = o.Single().BigIntegerFromBinaryString();
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i = 0;
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while (c.Count > 1)
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{
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var most = MostCommon(i, c);
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c = c.Where(r => r[i] != most).ToList();
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i++;
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}
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var co2 = c.Single().BigIntegerFromBinaryString();
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return o2 * co2;
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char MostCommon(int index, IReadOnlyCollection<string> report) =>
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report.Count(r => r[index] == '1') >= report.Count / 2.0 ? '1' : '0';
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}
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}
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