Added handling of invalid files and invalid Sudoku puzzles.

Author: kurtanr

SimpleSudokuSolver.Tests/Strategy/BacktrackingTests.cs

@@ -27,5 +27,26 @@ public void BacktrackingTest1()
       var sudokuPuzzle = solver.Solve(sudoku);
       Assert.That(sudokuPuzzle.IsSolved(), Is.True);
     }
+
+    [Test]
+    public void BacktrackingTest2()
+    {
+      var sudoku = new[,]
+      {
+        // Unsolvable, taken from: https://www.sudokudragon.com/unsolvable.htm
+        { 5,1,6,8,4,9,7,3,2 },
+        { 3,0,7,6,0,5,0,0,0 },
+        { 8,0,9,7,0,0,0,6,5 },
+        { 1,3,5,0,6,0,9,0,7 },
+        { 4,7,2,5,9,1,0,0,6 },
+        { 9,6,8,3,7,0,0,5,0 },
+        { 2,5,3,1,8,6,0,7,4 },
+        { 6,8,4,2,0,7,5,0,0 },
+        { 7,9,1,0,5,0,6,0,8 }
+      };
+
+      var sudokuPuzzle = solver.Solve(sudoku);
+      Assert.That(sudokuPuzzle.IsSolved(), Is.False);
+    }
   }
 }

SimpleSudokuSolver.UI/MainWindow.xaml.cs

@@ -3,6 +3,7 @@
 using SimpleSudokuSolver.PuzzleProviders;
 using SimpleSudokuSolver.UI.PuzzleProviders;
 using SimpleSudokuSolver.UI.ViewModel;
+using System;
 using System.IO;
 using System.Windows;
 
@@ -24,6 +25,7 @@ public MainWindow()
       viewModel.LoadGame += OnLoadGame;
       viewModel.SaveGame += OnSaveGame;
       viewModel.ExitGame += OnExitGame;
+      viewModel.InvalidSudokuLoaded += OnInvalidSudokuLoaded;
 
       DataContext = viewModel;
     }
@@ -35,14 +37,28 @@ private SudokuPuzzle OnLoadGame()
         CheckFileExists = true,
         Filter = DialogFilter
       };
-      if(openFileDialog.ShowDialog() == true)
+      if (openFileDialog.ShowDialog() == true)
       {
-        var sudoku = new SudokuFilePuzzleProvider(openFileDialog.FileName).GetPuzzle();
-        return new SudokuPuzzle(sudoku);
+        try
+        {
+          var sudoku = new SudokuFilePuzzleProvider(openFileDialog.FileName).GetPuzzle();
+          return new SudokuPuzzle(sudoku);
+        }
+        catch (Exception)
+        {
+          MessageBox.Show(this, $"Failed to load sudoku puzzle from file:\r\n{openFileDialog.FileName}", "Error loading Sudoku",
+            MessageBoxButton.OK, MessageBoxImage.Error, MessageBoxResult.OK, MessageBoxOptions.None);
+        }
       }
       return null;
     }
 
+    private void OnInvalidSudokuLoaded()
+    {
+      MessageBox.Show(this, $"Loaded file does not contain a valid sudoku puzzle\r\n(it is unsolvable).", "Error loading Sudoku",
+        MessageBoxButton.OK, MessageBoxImage.Error, MessageBoxResult.OK, MessageBoxOptions.None);
+    }
+
     private void OnSaveGame(SudokuPuzzle sudokuPuzzle)
     {
       var saveFileDialog = new SaveFileDialog

SimpleSudokuSolver.UI/ViewModel/MainViewModel.cs

@@ -20,8 +20,9 @@ public class MainViewModel : INotifyPropertyChanged
     public event Func<SudokuPuzzle> LoadGame;
     public event Action<SudokuPuzzle> SaveGame;
     public event Action ExitGame;
+    public event Action InvalidSudokuLoaded;
 
-    public Tuple<int,int> LastUpdatedCellIndex { get; private set; }
+    public Tuple<int, int> LastUpdatedCellIndex { get; private set; }
 
     private bool _showCandidates;
     public bool ShowCandidates
@@ -114,18 +115,31 @@ private void ExecuteNewGameCommand()
     private void ExecuteLoadGameCommand()
     {
       var loadGame = LoadGame;
-      if (loadGame != null)
+      if (loadGame == null)
       {
-        var sudokuPuzzle = loadGame();
-        if (sudokuPuzzle != null)
-        {
-          SudokuPuzzle = sudokuPuzzle;
-          SolvedSudokuPuzzle = _solver.Solve(sudokuPuzzle.ToIntArray());
-          LastUpdatedCellIndex = null;
-          Message = string.Empty;
-          UpdateStatusMessage();
-        }
+        return;
+      }
+
+      var sudokuPuzzle = loadGame();
+      if (sudokuPuzzle == null)
+      {
+        return;
+      }
+
+      try
+      {
+        SolvedSudokuPuzzle = _solver.Solve(sudokuPuzzle.ToIntArray());
       }
+      catch (Exception)
+      {
+        InvalidSudokuLoaded?.Invoke();
+        return;
+      }
+
+      SudokuPuzzle = sudokuPuzzle;
+      LastUpdatedCellIndex = null;
+      Message = string.Empty;
+      UpdateStatusMessage();
     }
 
     private void ExecuteSaveGameCommand()
@@ -225,11 +239,11 @@ public void UpdateStatusMessage()
       }
 
       var sb = new StringBuilder("Values left: ");
-      for(int i = 1; i <= SudokuPuzzle.NumberOfRowsOrColumnsInPuzzle; i++)
+      for (int i = 1; i <= SudokuPuzzle.NumberOfRowsOrColumnsInPuzzle; i++)
       {
         var numberOfValuesLeft = SudokuPuzzle.NumberOfRowsOrColumnsInPuzzle - SudokuPuzzle.Cells.OfType<Cell>().Count(x => x.Value == i);
         var separator = (i == SudokuPuzzle.NumberOfRowsOrColumnsInPuzzle) ? string.Empty : ",";
-        if(numberOfValuesLeft > 0)
+        if (numberOfValuesLeft > 0)
           sb.Append($"{i} x{numberOfValuesLeft}{separator} ");
       }