2018 Day05 Part1 solved

Solutions/2018/Day05.cs

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+using System.Text;
+
+namespace AdventOfCode.Solutions._2018;
+
+/// <summary>
+/// Day 05: Alchemical Reduction
+/// https://adventofcode.com/2018/day/05
+/// </summary>
+[Description("Alchemical Reduction")]
+public sealed partial class Day05 {
+	private const int OFFSET = 'a' - 'A';
+
+	public static string Part1(string[] input, params object[]? _) => Solution1(input).ToString();
+	public static string Part2(string[] input, params object[]? _) => Solution2(input).ToString();
+
+	private static int Solution1(string[] input) {
+		string polymer = input[0];
+
+		int currentLength;
+		do {
+			StringBuilder newPolymer = new();
+			currentLength = polymer.Length;
+			for (int i = 0; i < polymer.Length; i++) {
+				if (i < polymer.Length - 1 && (polymer[i] + OFFSET == polymer[i + 1] || polymer[i] == polymer[i + 1] + OFFSET)) {
+					i++;
+				} else {
+					_ = newPolymer.Append(polymer[i]);
+				}
+			}
+			polymer = newPolymer.ToString();
+		} while (polymer.Length != 0 && polymer.Length != currentLength);
+
+		return polymer.Length;
+	}
+
+	private static string Solution2(string[] input) {
+		//string inputLine = input[0];
+		//List<string> inputs = input.ToList();
+		return "** Solution not written yet **";
+	}
+}

Tests/2018/Tests_05.cs

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+namespace AdventOfCode.Tests.Year2018;
+
+public class Tests_05_Alchemical_Reaction
+{
+	const int DAY = 5;
+
+	[Theory]
+	[InlineData("aA", 0)]
+	[InlineData("abBA", 0)]
+	[InlineData("abAB", 4)]
+	[InlineData("aabAAB", 6)]
+	[InlineData("dabAcCaCBAcCcaDA", 10)]
+	public void Part1(string input, int expected)
+	{
+		_ = int.TryParse(SolutionRouter.SolveProblem(YEAR, DAY, PART1, input), out int actual);
+		Assert.Equal(expected, actual);
+	}
+
+	[Theory]
+	[InlineData("aA", 9999)]
+	public void Part2(string input, int expected)
+	{
+		_ = int.TryParse(SolutionRouter.SolveProblem(YEAR, DAY, PART2, input), out int actual);
+		Assert.Equal(expected, actual);
+	}
+}