chore: add some notes

src/EndMove.Sudoku.Solver.Core/Algorithms/BackTrackingSolver.cs

@@ -4,6 +4,12 @@ public class BackTrackingSolver : SolverBase
 {
     public BackTrackingSolver(Action<int[,]> displayBoard) : base(displayBoard) { }
 
+    /**
+     * note for future me :
+     * - Maybe pre-process the board to get the empty cells and already know used values per row, col and box
+     * - Maybe keep a track of the current index to avoid searching for the next empty cell in the all 2d array
+     * - Maybe avoid using negation
+     */
     public override (bool, int[,]) Solve(int[,] board)
     {
         int row = -1, col = -1;

src/EndMove.Sudoku.Solver.Core/Program.cs

@@ -58,7 +58,9 @@ namespace EndMove.Sudoku.Solver.Core
 
             SudokuUtils.TwoDTo1D(store[0], out int[] sudoku1D);
             SudokuUtils.DisplayBoard(sudoku1D);
+            // TODO improve 2D backtracking solver
             // TODO 1D solver with backtracking
+            // TODO Add time measurement
 
             ISolver solver = new BackTrackingSolver(SudokuUtils.DisplayBoard);
             var (status, lol) = solver.Solve(store[0]);