56 lines
1.4 KiB
C#
56 lines
1.4 KiB
C#
namespace aoc2020;
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/// <summary>
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/// Day 10: <see href="https://adventofcode.com/2020/day/10" />
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/// </summary>
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public sealed class Day10 : Day
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{
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private readonly int[] _adapters;
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private readonly long[] _memo;
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public Day10() : base(10, "Adapter Array")
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{
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var parsed = Input.Select(int.Parse).ToArray();
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// add socket and device to the list
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_adapters = parsed.Concat(new[] { 0, parsed.Max() + 3 }).OrderBy(i => i).ToArray();
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_memo = new long[_adapters.Length];
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}
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private long Connections(int i)
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{
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if (i == _adapters.Length - 1) _memo[i] = 1;
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if (_memo[i] > 0) return _memo[i];
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for (var j = i + 1; j <= i + 3 && j < _adapters.Length; j++)
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if (_adapters[j] - _adapters[i] <= 3)
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_memo[i] += Connections(j);
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return _memo[i];
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}
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public override string Part1()
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{
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var ones = 0;
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var threes = 0;
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for (var i = 0; i < _adapters.Length - 1; i++)
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switch (_adapters[i + 1] - _adapters[i])
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{
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case 1:
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ones++;
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break;
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case 3:
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threes++;
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break;
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default: throw new Exception("something went wrong");
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}
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return $"{ones * threes}";
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}
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public override string Part2()
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{
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return $"{Connections(0)}";
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}
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}
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