54 lines
1.8 KiB
C#
54 lines
1.8 KiB
C#
namespace AOC2020;
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/// <summary>
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/// Day 19: <a href="https://adventofcode.com/2020/day/19" />
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/// </summary>
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public sealed class Day19() : Day(2020, 19, "Monster Messages")
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{
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private string[]? _messages;
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private Dictionary<string, string[][]>? _rules;
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private Stack<string>? _stack;
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public override void ProcessInput()
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{
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_rules = Input.TakeWhile(l => !string.IsNullOrWhiteSpace(l))
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.Select(l => l.Split(':'))
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.Select(a => (key: a[0],
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val: a[1].Split('|', StringSplitOptions.RemoveEmptyEntries)
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.Select(s => s.Split(' ', StringSplitOptions.RemoveEmptyEntries)).ToArray()))
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.ToDictionary(a => a.key, a => a.val);
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_messages = Input.Skip(_rules.Count + 1).ToArray();
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_stack = new();
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}
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private string MakeRegexExpression(string key)
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{
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if (_stack!.Count(s => s == key) > 10) return "x";
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_stack!.Push(key);
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var sub = string.Join("|", _rules![key].Select(test => test.Length switch
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{
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1 => test[0][0] == '"' ? test[0].Trim('"') : MakeRegexExpression(test[0]),
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_ => string.Join(string.Empty, test.Select(MakeRegexExpression))
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}));
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_stack.Pop();
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return _rules[key].Length > 1 ? $"({sub})" : sub;
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}
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public override object Part1()
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{
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var exp = new Regex($"^{MakeRegexExpression("0")}$");
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return _messages!.Count(m => exp.IsMatch(m));
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}
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public override object Part2()
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{
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// fix rules 8 and 11
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_rules!["8"] = new[] { new[] { "42" }, new[] { "42", "8" } };
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_rules["11"] = new[] { new[] { "42", "31" }, new[] { "42", "11", "31" } };
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var exp = new Regex($"^{MakeRegexExpression("0")}$");
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return _messages!.Count(m => exp.IsMatch(m));
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}
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}
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