61 lines
1.5 KiB
C#
61 lines
1.5 KiB
C#
namespace aoc2021;
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/// <summary>
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/// Day 3: <see href="https://adventofcode.com/2021/day/3"/>
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/// </summary>
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public sealed class Day03 : Day
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{
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private readonly List<string> _report;
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public Day03() : base(3, "Binary Diagnostic")
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{
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_report = Input.ToList();
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}
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public override string 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 = Convert.ToInt32(g.ToString(), 2);
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var epsilon = Convert.ToInt32(e.ToString(), 2);
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return $"{gamma * epsilon}";
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}
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public override string Part2()
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{
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var o = _report;
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var c = _report;
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char MostCommon(int i, IReadOnlyCollection<string> report) =>
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report.Count(r => r[i] == '1') >= report.Count / 2.0 ? '1' : '0';
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var i = 0;
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while (o.Count > 1)
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{
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o = o.Where(r => r[i] == MostCommon(i, o)).ToList();
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i++;
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}
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var o2 = Convert.ToInt64(o.Single(), 2);
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i = 0;
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while (c.Count > 1)
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{
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c = c.Where(r => r[i] != MostCommon(i, c)).ToList();
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i++;
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}
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var co2 = Convert.ToInt64(c.Single(), 2);
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return $"{o2 * co2}";
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}
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}
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