Day 4

This is more what I was expecting for the first few days.

src/04.cs

@@ -0,0 +1,71 @@
+namespace aoc2023;
+
+internal class Day04 : Day
+{
+    private List<List<int>> cardNums = new();
+    private List<List<int>> winningNums = new();
+
+    internal override void Parse()
+    {
+        var lines = Util.Parsing.ReadAllLines($"{GetDay()}");
+        foreach (var line in lines)
+        {
+            var split = line.Split('|');
+            var cardsplit = split[0].Split(':');
+            cardNums.Add(cardsplit[1].Split(' ').Where(s => !string.IsNullOrEmpty(s)).Select(int.Parse).ToList());
+            winningNums.Add(split[1].Split(' ').Where(s => !string.IsNullOrEmpty(s)).Select(int.Parse).ToList());
+        }
+    }
+
+    internal override string Part1()
+    {
+        long total = 0;
+        for (int cardIdx = 0; cardIdx < cardNums.Count; cardIdx++)
+        {
+            long cardtotal = 0;
+            foreach (var num in cardNums[cardIdx])
+            {
+                if (winningNums[cardIdx].Contains(num))
+                {
+                    if (cardtotal == 0)
+                    {
+                        cardtotal = 1;
+                    }
+                    else
+                    {
+                        cardtotal *= 2;
+                    }
+                }
+            }
+
+            total += cardtotal;
+        }
+
+        return $"Total value of cards counted once: <+white>{total}";
+    }
+
+    internal override string Part2()
+    {
+        Dictionary<int, int> cardCopies = new();
+        for (int i = 0; i < cardNums.Count; i++)
+        {
+            cardCopies.Add(i, 1);
+        }
+
+        for (int cardIdx = 0; cardIdx < cardNums.Count; cardIdx++)
+        {
+            int numMatches = 0;
+            foreach (var num in cardNums[cardIdx])
+            {
+                if (winningNums[cardIdx].Contains(num))
+                {
+                    numMatches++;
+                    cardCopies[cardIdx + numMatches] += cardCopies[cardIdx];
+                }
+            }
+        }
+
+        long total = cardCopies.Sum(c => c.Value);
+        return $"Total number of cards: <+white>{total}";
+    }
+}