day(25): Done!

src/AdventOfCode/Day25.cs

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+using System.Collections.Generic;
+using System.Linq;
+
+namespace AdventOfCode
+{
+    /// <summary>
+    /// Solver for Day 25
+    /// </summary>
+    public class Day25
+    {
+        public int Part1(string input)
+        {
+            List<Schematic> locks = [];
+            List<Schematic> keys = [];
+
+            foreach (string chunk in input.TrimEnd().Split("\n\n"))
+            {
+                string[] lines = chunk.Split("\n");
+
+                bool isLock = lines[0] == "#####";
+
+                IEnumerable<string> rows = isLock ? lines.Skip(1) : lines.Reverse().Skip(1);
+
+                int height0 = 0, height1 = 0, height2 = 0, height3 = 0, height4 = 0;
+
+                foreach (string row in rows)
+                {
+                    height0 += row[0] == '#' ? 1 : 0;
+                    height1 += row[1] == '#' ? 1 : 0;
+                    height2 += row[2] == '#' ? 1 : 0;
+                    height3 += row[3] == '#' ? 1 : 0;
+                    height4 += row[4] == '#' ? 1 : 0;
+                }
+
+                if (isLock)
+                {
+                    locks.Add(new Schematic(height0, height1, height2, height3, height4));
+                }
+                else
+                {
+                    keys.Add(new Schematic(height0, height1, height2, height3, height4));
+                }
+            }
+
+            return keys.Sum(k => locks.Count(l => k.Height0 + l.Height0 < 6
+                                               && k.Height1 + l.Height1 < 6
+                                               && k.Height2 + l.Height2 < 6
+                                               && k.Height3 + l.Height3 < 6
+                                               && k.Height4 + l.Height4 < 6));
+        }
+
+        private record Schematic(int Height0, int Height1, int Height2, int Height3, int Height4);
+    }
+}

tests/AdventOfCode.Tests/Day25Tests.cs

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+using System.IO;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace AdventOfCode.Tests
+{
+    public class Day25Tests
+    {
+        private readonly ITestOutputHelper output;
+        private readonly Day25 solver;
+
+        public Day25Tests(ITestOutputHelper output)
+        {
+            this.output = output;
+            this.solver = new Day25();
+        }
+
+        private static string GetRealInput()
+        {
+            string input = File.ReadAllText("inputs/day25.txt");
+            return input;
+        }
+
+        [Fact]
+        public void Part1_RealInput_ProducesCorrectResponse()
+        {
+            var expected = 3021;
+
+            var result = solver.Part1(GetRealInput());
+            output.WriteLine($"Day 25 - Part 1 - {result}");
+
+            Assert.Equal(expected, result);
+        }
+    }
+}