86 lines
2.3 KiB
C#
86 lines
2.3 KiB
C#
namespace aoc2021;
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/// <summary>
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/// Day 8: <see href="https://adventofcode.com/2021/day/8"/>
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/// </summary>
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public sealed class Day08 : Day
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{
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private static readonly List<char[]> PossibleMappings =
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"abcdefg".ToCharArray().Permute().Select(m => m.ToArray()).ToList();
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public Day08() : base(8, "Seven Segment Search")
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{
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}
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private static int MatchDigit(string lit) =>
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lit switch
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{
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"1110111" => 0,
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"0010010" => 1,
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"1011101" => 2,
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"1011011" => 3,
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"0111010" => 4,
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"1101011" => 5,
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"1101111" => 6,
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"1010010" => 7,
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"1111111" => 8,
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"1111011" => 9,
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_ => -1
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};
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private static int Decode(string line)
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{
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var s = line.Split(" | ").Select(s => s.Split(' ')).ToList();
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int i;
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char[] lit;
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for (i = 0; i < PossibleMappings.Count; i++)
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{
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var matches = 0;
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var failed = false;
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foreach (var signal in s[0])
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{
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lit = "0000000".ToCharArray();
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foreach (var c in signal)
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lit[Array.IndexOf(PossibleMappings[i], c)] = '1';
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var match = MatchDigit(new(lit));
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if (match == -1)
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{
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failed = true;
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break;
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}
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matches++;
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}
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if (failed) continue;
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if (matches == 10) break;
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}
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if (i == PossibleMappings.Count)
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{
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throw new("no mapping found");
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}
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var digits = new StringBuilder();
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foreach (var o in s[1])
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{
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lit = "0000000".ToCharArray();
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foreach (var c in o)
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lit[Array.IndexOf(PossibleMappings[i], c)] = '1';
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digits.Append(MatchDigit(new(lit)));
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}
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return int.Parse(digits.ToString());
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}
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public override object Part1() =>
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Input
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.Select(line => line.Split(" | ")[1].Split(' '))
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.Select(outputs => outputs.Count(o => new[] { 2, 3, 4, 7 }.Contains(o.Length)))
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.Sum();
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public override object Part2() => Input.Select(Decode).Sum();
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}
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