public void SolveSudoku(char[][] board)
{
var placeHoldersCount = 0;
var placeHolders = new bool[9][];
var numberStatuses = new NumberStatus[9];
for (int i = 0; i < 9; i++)
{
numberStatuses[i] = new NumberStatus();
}
for (int i = 0; i < 9; i++)
{
placeHolders[i] = new bool[9];
for (int j = 0; j < 9; j++)
{
if (board[i][j] == '.')
{
placeHoldersCount++;
placeHolders[i][j] = true;
}
else
{
int val = board[i][j] - '1';
numberStatuses[val].UsedInColumns[j] = true;
numberStatuses[val].UsedInRows[i] = true;
numberStatuses[val].UsedInSquares[NumberStatus.GetSquareNumber(i, j)] = true;
}
}
}
SolveSudokuImpl(board, placeHolders, numberStatuses, placeHoldersCount);
}
private bool SolveSudokuImpl(char[][] board, bool[][] placeHolders, NumberStatus[] numberStatus, int numbersLeft)
{
if (numbersLeft == 0)
{
return(CheckSudokuSolved(board));
}
for (int i = 0; i < 9; i++)
{
for (int j = 0; j < 9; j++)
{
if (!placeHolders[i][j] || board[i][j] != '.')
{
continue;
}
for (char c = '1'; c <= '9'; c++)
{
var val = c - '1';
if (numberStatus[val].UsedInRows[i] ||
numberStatus[val].UsedInColumns[j] ||
numberStatus[val].UsedInSquares[NumberStatus.GetSquareNumber(i, j)])
{
continue;
}
var prevUsedInRows = numberStatus[val].UsedInRows[i];
var prevUsedInColumns = numberStatus[val].UsedInColumns[j];
var prevUsedInSquares = numberStatus[val].UsedInSquares[NumberStatus.GetSquareNumber(i, j)];
board[i][j] = c;
if (SolveSudokuImpl(board, placeHolders, numberStatus, numbersLeft - 1))
{
return(true);
}
board[i][j] = '.';
numberStatus[val].UsedInRows[i] = prevUsedInRows;
numberStatus[val].UsedInColumns[j] = prevUsedInColumns;
numberStatus[val].UsedInSquares[NumberStatus.GetSquareNumber(i, j)] = prevUsedInSquares;
}
}
}
return(false);
}