Added Utils namespace

Utils/Extensions.cs

@@ -0,0 +1,32 @@
+namespace AdventOfCode.Utils;
+
+public static class Extensions
+{
+    /// <summary>
+    /// Returns a slice of the given list
+    /// </summary>
+    /// <param name="list">The list you pretend to slice</param>
+    /// <param name="startIndex">The first index of the slice</param>
+    /// <param name="endIndex">The index after the last index of the slice</param>
+    /// <returns></returns>
+    public static List<T> Sublist<T>(this List<T> list, int startIndex, int endIndex)
+    {
+        List<T> result = new List<T>();
+        for (int i = startIndex; i < endIndex; i++)
+            result.Add(list[i]);
+        return result;
+    }
+
+    /// <summary>
+    /// Returns a column of a give matrix list
+    /// </summary>
+    /// <param name="list">2 dimensions list</param>
+    /// <param name="column">Column index</param>
+    /// <returns></returns>
+    public static List<T> GetColumn<T>(this List<List<T>> list, int column)
+    {
+        List<T> result = new List<T>();
+        foreach (List<T> row in list) result.AddRange(row.Where((t, i) => i == column));
+        return result;
+    }
+}