Day 15

Not sure how I feel about this one. I don't mind a "day off" of sorts, but there were just so. many. words in the puzzle that boiled down to such a straightforward implementation. I guess this is practice of "implement detailed requirements exactly to spec" or something.

advent-of-code-2023.csproj

@@ -60,6 +60,8 @@
 	  <EmbeddedResource Include="inputs\13a.txt" />
 	  <EmbeddedResource Include="inputs\14.txt" />
 	  <EmbeddedResource Include="inputs\14a.txt" />
+	  <EmbeddedResource Include="inputs\15.txt" />
+	  <EmbeddedResource Include="inputs\15a.txt" />
 	</ItemGroup>
 
 	<ItemGroup>

inputs/15a.txt

@@ -0,0 +1 @@
+rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7

src/15.cs

@@ -0,0 +1,91 @@
+namespace aoc2023;
+
+internal class Day15 : Day
+{
+    class lens
+    {
+        public string label = string.Empty;
+        public int length;
+
+        public override string ToString() => $"[{label} {length}]";
+    }
+
+    private List<string> sequence = [];
+    internal override void Parse()
+    {
+        var str = Util.Parsing.ReadAllText($"{GetDay()}");
+        sequence = [.. str.Split(',')];
+    }
+
+    private byte GetSequenceHash(string seq)
+    {
+        int val = 0;
+        foreach (var ch in seq)
+        {
+            val += ch;
+            val *= 17;
+            val %= 256;
+        }
+
+        return (byte)val;
+    }
+
+    internal override string Part1()
+    {
+        long total = sequence.Sum(s => GetSequenceHash(s));
+        return $"Sum of each sequence's hash: <+white>{total}";
+    }
+
+    internal override string Part2()
+    {
+        List<lens>[] boxes = new List<lens>[256];
+        for (int i = 0; i < 256; i++)
+        {
+            boxes[i] = [];
+        }
+
+        foreach (var seq in sequence)
+        {
+            var opIdx = seq.IndexOfAny(['-', '=']);
+            var label = seq[..opIdx];
+            int box = GetSequenceHash(label);
+            var op = seq[opIdx];
+            if (op == '=')
+            {
+                int len = int.Parse(seq[(opIdx + 1)..]);
+                int idx = boxes[box].FindIndex(l => l.label == label);
+                if (idx >= 0)
+                {
+                    boxes[box][idx].length = len;
+                }
+                else
+                {
+                    boxes[box].Add(new lens(){label = label, length = len});
+                }
+
+                continue;
+            }
+
+            boxes[box].RemoveAll(l => l.label == label);
+        }
+
+        long total = 0;
+        for (int i = 0; i < 256; i++)
+        {
+            if (!boxes[i].Any())
+            {
+                continue;
+            }
+
+            for (int j = 0; j < boxes[i].Count; j++)
+            {
+                long boxval = i + 1;
+                boxval *= (j + 1);
+                boxval *= boxes[i][j].length;
+                total += boxval;
+            }
+        }
+
+        return $"Focusing power of final configuration: <+white>{total}";
+    }
+}