46 lines
1.1 KiB
C#
46 lines
1.1 KiB
C#
namespace AOC2020;
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/// <summary>
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/// Day 15: <a href="https://adventofcode.com/2020/day/15" />
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/// </summary>
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public sealed class Day15() : Day(2020, 15, "Rambunctious Recitation")
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{
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private int[]? _turns;
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private int _current;
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private int _i;
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public override void ProcessInput()
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{
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var initial = Input.First().Split(',').Select(int.Parse).ToArray();
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_turns = new int[30_000_000];
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// seed array with initial values
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for (_i = 1; _i < initial.Length + 1; _i++)
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_turns[initial[_i - 1]] = _i;
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}
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public override object Part1()
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{
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for (; _i != 2020; _i++)
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{
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var next = _turns![_current] > 0 ? _i - _turns[_current] : 0;
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_turns[_current] = _i;
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_current = next;
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}
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return _current;
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}
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public override object Part2()
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{
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for (; _i != 30_000_000; _i++)
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{
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var next = _turns![_current] > 0 ? _i - _turns[_current] : 0;
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_turns[_current] = _i;
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_current = next;
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}
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return _current;
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}
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}
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