public bool HasSudokuUniqueSolution(SudokuPuzzle sudoku)
{
// sudokus with 16 or less determinded fields cannot have a unique solution
// source: https://www.technologyreview.com/s/426554/mathematicians-solve-minimum-sudoku-problem/
bool ret = (sudoku.GetSetFields()?.Count > 16);
if (ret)
{
// solve sudoku (gets one solution out of possibly many solutions)
var solution = SolveSudoku(sudoku);
ret = (solution != null);
if (ret)
{
var temp = (SudokuPuzzle)sudoku.Clone();
// go through all empty fields (filled out fields are ignored)
while (ret && !temp.IsSolved())
{
// choose a free field with a minimum amount of remaining possibilities
int minPossibleValuesCount = temp.GetFreeFields().Select(x => x.GetPossibleValuesCount()).Min();
var field = temp.GetFreeFields().Where(x => x.GetPossibleValuesCount() == minPossibleValuesCount).ChooseRandom();
// check if the field is determined; if not, there is a second solution => return false
ret = isFieldDetermined(temp, solution, field);
// apply the determined value to the sudoku => less possibilities
field.SetValue(solution.Fields[field.RowIndex, field.ColumnIndex].Value);
}
}
}
return(ret);
}
public SudokuPuzzle GenerateSudoku(SudokuDifficuty difficulty, int length = 9)
{
// get randomly filled out sudoku
SudokuPuzzle solution = SolveSudoku(new SudokuPuzzle());
SudokuPuzzle sudoku = (SudokuPuzzle)solution.Clone();
// check how many fields need to be removed (depending on desired difficulty)
int fieldsToRemove = ((length * length) - (int)difficulty);
while (fieldsToRemove > 0)
{
int freeFieldsCount = sudoku.GetFreeFields().Count;
foreach (var field in sudoku.GetSetFields().Shuffle())
{
if (fieldsToRemove > 0 && isFieldDetermined(sudoku, solution, field.RowIndex, field.ColumnIndex))
{
field.SetValue(0);
fieldsToRemove--;
}
}
// check if progress was made (if not => try with another sudoku puzzle)
if ((freeFieldsCount - sudoku.GetFreeFields().Count) == 0)
{
sudoku = GenerateSudoku(difficulty, length);
break;
}
}
// check if the generated sudoku is unique. if not create a new one.
return((HasSudokuUniqueSolution(sudoku)) ? sudoku : GenerateSudoku(difficulty, length));
}
protected SudokuPuzzle guessNextField(SudokuPuzzle sudoku, SudokuField field)
{
SudokuPuzzle result = null;
foreach (int value in field.GetPossibleValues().Shuffle())
{
// make copy of sudoku and try out possibility
var copy = (SudokuPuzzle)sudoku.Clone();
copy.Fields[field.RowIndex, field.ColumnIndex].SetValue(value);
if (copy.IsValid())
{
// go to next recursion level
result = solveSudokuRecursive(copy);
// pass correct solution to lower recursion levels
if (result != null)
{
break;
}
}
}
return(result);
}
private SudokuPuzzle tryNextLevel(SudokuPuzzle sudoku, int row, int column, IEnumerable <int> possibleValues)
{
SudokuPuzzle result = null;
// prepare row / column index for next recursion level
int nextRow = row;
int nextColumn = column;
incrementFieldIndices(ref nextRow, ref nextColumn, sudoku.Length);
foreach (int value in possibleValues)
{
// make copy of sudoku and try out possibility
var copy = (SudokuPuzzle)sudoku.Clone();
copy.Fields[row, column].SetValue(value);
if (copy.IsValid())
{
// go to next recursion level
result = solveSudokuRecursive(copy, nextRow, nextColumn);
// pass correct solution to lower recursion levels
if (result != null)
{
break;
}
}
}
return(result);
}
public void TestRemoveNumbers()
{
Assert.ThrowsException <ArgumentNullException>(() => SudokuGenerator.RemoveNumbers(null));
SudokuPuzzle sudoku = SudokuGenerator.AddNumbers(SudokuPuzzleTest.Size, SudokuPuzzleTest.Difficulty);
Console.WriteLine(sudoku);
SudokuPuzzle original = (SudokuPuzzle)sudoku.Clone();
SudokuGenerator.RemoveNumbers(sudoku);
Console.WriteLine(sudoku);
SudokuSolver.RecursiveSolve(sudoku);
Assert.AreEqual(original, sudoku);
}
/// <summary>
/// Solves the given <see cref="SudokuPuzzle"/>
/// </summary>
/// <param name="puzzle">The <see cref="SudokuPuzzle"/> being solved</param>
/// <returns>A list of <see cref="SudokuPuzzle"/>s that are solutions to the given <see cref="SudokuPuzzle"/></returns>
public List <SudokuPuzzle> Solve(SudokuPuzzle puzzle)
{
List <SudokuPuzzle> solutions = new List <SudokuPuzzle>();
Stack <SudokuPuzzle> puzzleStack = new Stack <SudokuPuzzle>();
puzzleStack.Push(puzzle.Clone());
while (puzzleStack.Count > 0)
{
try
{
SudokuPuzzle puzzleToSolve = puzzleStack.Pop();
if (puzzle.IsValid())
{
bool puzzleAdvanced = false;
do
{
puzzleAdvanced = false;
for (int i = 0; i < this.strategies.Count; ++i)
{
while (this.strategies[i].AdvancePuzzle(puzzleToSolve))
{
puzzleAdvanced = true;
}
}
}while (puzzleAdvanced);
if (puzzleToSolve.IsSolved() && puzzleToSolve.IsValid())
{
solutions.Add(puzzleToSolve);
if (solutions.Count > 1)
{
break;
}
}
else
{
foreach (SudokuPuzzle guess in this.Guess(puzzleToSolve))
{
puzzleStack.Push(guess);
}
}
}
}
catch (Exception)
{
}
}
return(solutions);
}
/// <summary>
/// Finds a <see cref="Cell"/> with the least possible values (other than solved <see cref="Cell"/>s),
/// and tries each possible puzzle using those values in that cell
/// </summary>
/// <param name="puzzle">The <see cref="SudokuPuzzle"/> being solved</param>
/// <returns>The puzzle solutions found from guessing</returns>
private List <SudokuPuzzle> Guess(SudokuPuzzle puzzle)
{
if (!puzzle.IsValid())
{
return(new List <SudokuPuzzle>());
}
Cell cellToGuessOn = null;
int x = -1;
int y = -1;
for (int i = 0; i < puzzle.Rows.Count; ++i)
{
for (int k = 0; k < puzzle.Rows[i].Count; ++k)
{
Cell cell = puzzle.Rows[i][k];
if (cell.Count > 1)
{
if (cellToGuessOn == null)
{
cellToGuessOn = cell;
x = i;
y = k;
}
else if (cellToGuessOn.Count > cell.Count)
{
cellToGuessOn = cell;
x = i;
y = k;
}
}
}
}
List <SudokuPuzzle> guesses = new List <SudokuPuzzle>();
if (cellToGuessOn != null)
{
foreach (int allowedValue in cellToGuessOn.AllowedValues.Keys)
{
SudokuPuzzle guess = puzzle.Clone();
guess.Rows[x][y].RemoveAllExcept(allowedValue);
guesses.Add(guess);
}
}
return(guesses);
}
private bool removeField(SudokuPuzzle sudoku, SudokuPuzzle solution)
{
foreach (SudokuField field in sudoku.GetSetFields().Shuffle())
{
// clone sudoku and set the field value to 0
SudokuPuzzle temp = (SudokuPuzzle)sudoku.Clone();
SudokuField tempField = temp.Fields[field.RowIndex, field.ColumnIndex];
tempField.SetValue(0);
if (HasSudokuUniqueSolution(temp))
{
field.SetValue(0);
return(true);
}
}
return(false);
}
public void TestClone()
{
string inputFilePath = "TestPuzzleInput.txt";
SudokuFiler filer = new SudokuFiler(inputFilePath);
SudokuPuzzle puzzle = filer.CreatePuzzle();
for (int i = 0; i < puzzle.Dimension * puzzle.Dimension; ++i)
{
if (puzzle.Rows[0][i].Count == 1)
{
int allowedValue = puzzle.Rows[0][i].AllowedValue;
if (allowedValue != 1)
{
allowedValue = 1;
}
else
{
++allowedValue;
}
puzzle.Rows[0][i].AddAllowedValue(allowedValue);
break;
}
}
SudokuPuzzle clonedPuzzle = puzzle.Clone();
for (int i = 0; i < puzzle.Dimension * puzzle.Dimension; ++i)
{
for (int k = 0; k < puzzle.Dimension * puzzle.Dimension; ++k)
{
Assert.IsTrue(puzzle.Rows[i][k].Count == clonedPuzzle.Rows[i][k].Count);
Assert.IsTrue(puzzle.Columns[i][k].Count == clonedPuzzle.Columns[i][k].Count);
Assert.IsTrue(puzzle.Blocks[i][k].Count == clonedPuzzle.Blocks[i][k].Count);
foreach (int allowedValue in puzzle.Rows[i][k].AllowedValues.Keys)
{
Assert.IsTrue(clonedPuzzle.Rows[i][k].AllowedValues.ContainsKey(allowedValue));
}
}
}
}
public bool HasSudokuUniqueSolution(SudokuPuzzle sudoku)
{
// solve sudoku (gets one solution out of many solutions)
var solution = SolveSudoku(sudoku);
bool ret = false;
if (solution != null)
{
int row = 0;
int column = 0;
SudokuField originalField;
var temp = (SudokuPuzzle)sudoku.Clone();
// go through all empty fields (filled out fields are ignored)
while ((originalField = getNextFreeField(temp, ref row, ref column)) != null)
{
// get value of field from solution
int solutionValue = solution.Fields[row, column].Value;
// try to solve the sudoku again, but without the value from the solution
var possibleValues = originalField.GetPossibleValues().Except(new int[] { solutionValue }).ToArray();
var secondSolution = tryNextLevel(temp, row, column, possibleValues);
// if there is a second solution, the sudoku has definitely not a unique solution => leave with false
if (secondSolution != null && !solution.Equals(secondSolution))
{
goto Leave;
}
// increment row / column index => this avoids checking a field twice
incrementFieldIndices(ref row, ref column, sudoku.Length);
}
}
// all empty fields have a unique solution => there is no second solution => leave with true
ret = true;
Leave:
return(ret);
}
private SudokuPuzzle solveSudokuRecursive(SudokuPuzzle original, int row = 0, int column = 0)
{
SudokuPuzzle result = null;
SudokuField field;
// make a copy of overloaded sudoku
var copy = (SudokuPuzzle)original.Clone();
// eliminate possibilities in copy / fill out fields with a single remaining possibility
copy.EliminatePossibilities();
// go through all empty fields
while ((field = getNextFreeField(copy, ref row, ref column)) != null)
{
var possibleValues = field.GetPossibleValues().Shuffle();
if (possibleValues.Count > 1)
{
// case with multiple remaining possibilities => try each of them with brute force
result = tryNextLevel(copy, row, column, possibleValues);
goto Leave;
}
else if (possibleValues.Count == 1)
{
// case with a single remaining possibility => set value
field.SetValueIfDetermined();
}
else
{
result = null;
goto Leave;
}
}
result = copy.IsSolved() ? copy : result;
Leave:
return(result);
}
public SudokuPuzzle GenerateSudoku(SudokuDifficuty difficulty, int length = 9)
{
// get randomly filled out sudoku
SudokuPuzzle source = SolveSudoku(new SudokuPuzzle());
SudokuPuzzle result;
int i;
int fieldsToRemove = ((length * length) - (int)difficulty);
//DateTime genStart = DateTime.Now;
//Console.WriteLine($"====================================================");
do
{
result = (SudokuPuzzle)source.Clone();
result.GetFields1D().ChooseRandom().SetValue(0);
for (i = 0; i < fieldsToRemove; i++)
{
//DateTime start = DateTime.Now;
if (!removeField(result, source))
{
break;
}
//DateTime end = DateTime.Now;
//Console.WriteLine($"iteration { i } took { (end - start).TotalMilliseconds } ms");
}
//if (i < fieldsToRemove) { Console.WriteLine($"generator failed"); }
//else { Console.WriteLine($"generator successful (total time elapsed: { (DateTime.Now - genStart).TotalMilliseconds } ms)"); }
}while (i < fieldsToRemove);
//Console.WriteLine($"====================================================");
return(result);
}
protected SudokuPuzzle solveSudokuRecursive(SudokuPuzzle original)
{
// make a copy of overloaded sudoku
var copy = (SudokuPuzzle)original.Clone();
SudokuPuzzle result = copy;
// eliminate possibilities in copy / fill out fields with a single remaining possibility
copy.EliminatePossibilities();
// go through all empty fields
if (copy.GetFreeFields().Count > 0)
{
// choose a free field with a minimum amount of possibilities
int minPossibleValuesCount = copy.GetFreeFields().Select(x => x.GetPossibleValuesCount()).Min();
var field = copy.GetFreeFields().Where(x => x.GetPossibleValuesCount() == minPossibleValuesCount).ChooseRandom();
var possibleValues = field.GetPossibleValues().Shuffle();
if (possibleValues.Count > 1)
{
// case with multiple remaining possibilities => try each of them with brute force
result = guessNextField(copy, field);
}
else if (possibleValues.Count == 1)
{
// case with a single remaining possibility => set value
field.SetValueIfDetermined();
}
else
{
// sudoku has no valid solution => go back to the previous recursion step
result = null;
}
}
return(result);
}
