day 13 part 1

AdventOfCode/Day13.cs

@@ -0,0 +1,86 @@
+
+namespace AdventOfCode;
+
+public class Day13 : BaseDay
+{
+    string[][] _input;
+
+    public Day13() 
+    {
+        string all = File.ReadAllText(InputFilePath);
+        _input = all.Split(Environment.NewLine + Environment.NewLine, StringSplitOptions.RemoveEmptyEntries)
+            .Select(p => p.Split(Environment.NewLine))
+            .ToArray();
+    }
+
+    public override ValueTask<string> Solve_1()
+    {
+        int sum = 0;
+        for (int i = 0; i < _input.Length; ++i)
+        {
+            sum += GetMirror(_input[i], Direction.Vertical);
+            sum += GetMirror(_input[i], Direction.Horizontal) * 100;
+        }
+
+        return new(sum.ToString());
+    }
+
+    private int GetMirror(string[] pattern, Direction direction)
+    {
+        int length = direction == Direction.Vertical ? pattern[0].Length : pattern.Length;
+        for (int i = 0; i < length - 1; ++i)
+        {
+            if (IsMirror(pattern, i, direction, length))
+            {
+                return i + 1;
+            }
+        }
+
+        return 0;
+    }
+
+    private bool IsMirror(string[] pattern, int splitAfter, Direction direction, int length)
+    {
+        int a = splitAfter;
+        int b = splitAfter + 1;
+
+        while (a >= 0 && b < length)
+        {
+            if (!(direction == Direction.Vertical ? ColumnsEqual(pattern, a, b) : RowEqual(pattern, a, b)))
+            { 
+                return false;
+            }
+            a--;
+            b++;
+        }
+        return true;
+    }
+
+    private bool ColumnsEqual(string[] pattern, int a, int b)
+    {
+        for (int i = 0; i < pattern.Length; ++i)
+        {
+            if (pattern[i][a] != pattern[i][b])
+            { 
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private bool RowEqual(string[] pattern, int a, int b)
+    {
+        return pattern[a] == pattern[b];
+    }
+
+    public override ValueTask<string> Solve_2()
+    {
+        return new("TBD");
+    }
+
+    private enum Direction
+    { 
+        Horizontal,
+        Vertical
+    }
+}