public void Solve(Grid grid)
{
var boxCols = grid.GetBoxColumns();
var boxRows = grid.GetBoxRows();
for (var digit = 1; digit <= 9; ++digit)
{
for (var boxCol = 1; boxCol <= 3; ++boxCol)
{
var leftColumn = boxCols[boxCol].Item1;
var middleColumn = boxCols[boxCol].Item1 + 1;
var rightColumn = boxCols[boxCol].Item2;
var possibleDigitBoxColumns = grid.FindThePotentialDigitInTheBoxColumns(boxRows, digit, leftColumn, middleColumn, rightColumn);
if (possibleDigitBoxColumns.Values.All(v => v.Count != 1)) continue;
// Where there is only one possible column for a digit within the box, remove it from that column for other boxes
foreach (var possibleDigitBoxColumn in possibleDigitBoxColumns)
{
if (possibleDigitBoxColumn.Value.Count != 1) continue;
var columnToClear = possibleDigitBoxColumn.Value[0];
for (var otherBoxRow = 1; otherBoxRow <= 3; ++otherBoxRow)
{
if (otherBoxRow == possibleDigitBoxColumn.Key) continue;
for (var rowIdx = boxRows[otherBoxRow].Item1;
rowIdx <= boxRows[otherBoxRow].Item2;
++rowIdx)
{
if (grid.Squares[rowIdx, columnToClear].IsSolved) continue;
grid.Squares[rowIdx, columnToClear].RemovePossibleDigit(digit);
}
}
}
}
}
}
public void Solve(Grid grid)
{
const int IgnoreColumn = -1;
var boxRows = grid.GetBoxRows();
var boxCols = grid.GetBoxColumns();
for (var digit = 1; digit <= 9; ++digit)
{
for (var boxCol = 1; boxCol <= 3; ++boxCol)
{
var leftColumn = boxCols[boxCol].Item1;
var middleColumn = boxCols[boxCol].Item1 + 1;
var rightColumn = boxCols[boxCol].Item2;
var possibleDigitBoxColumns = grid.FindThePotentialDigitInTheBoxColumns(boxRows, digit, leftColumn, middleColumn, rightColumn);
var countOfColumnBoxPairs = possibleDigitBoxColumns.Count(pb => pb.Value.Count == 2);
if (countOfColumnBoxPairs < 2) continue;
foreach (var possibleDigitBoxColumn in possibleDigitBoxColumns)
{
var firstBox = possibleDigitBoxColumn.Key;
if (possibleDigitBoxColumn.Value.Count == 0) continue;
if (possibleDigitBoxColumn.Value.Count > 2) continue;
var firstColumn = possibleDigitBoxColumn.Value[0];
var secondColumn = possibleDigitBoxColumn.Value.Count > 1
? possibleDigitBoxColumn.Value[1]
: IgnoreColumn;
foreach (var otherDigitBoxColumn in possibleDigitBoxColumns)
{
if (otherDigitBoxColumn.Key == possibleDigitBoxColumn.Key) continue;
if (otherDigitBoxColumn.Value.Count > 2) continue;
if (otherDigitBoxColumn.Value.Count == 0) continue;
if (!otherDigitBoxColumn.Value.Contains(firstColumn)) continue;
if (secondColumn != IgnoreColumn && !otherDigitBoxColumn.Value.Contains(secondColumn)) continue;
var secondBox = otherDigitBoxColumn.Key;
if (secondColumn == IgnoreColumn && otherDigitBoxColumn.Value.Count > 1)
{
secondColumn = otherDigitBoxColumn.Value[1];
}
// Digit is restricted to two particular columns between two boxes
// Therefore remove from the third
var thirdBox = possibleDigitBoxColumns.Single(pb => pb.Key != firstBox && pb.Key != secondBox);
for (var rowIdx = boxRows[thirdBox.Key].Item1;
rowIdx <= boxRows[thirdBox.Key].Item2;
++ rowIdx)
{
grid.Squares[rowIdx, firstColumn].RemovePossibleDigit(digit);
if (secondColumn != IgnoreColumn)
{
grid.Squares[rowIdx, secondColumn].RemovePossibleDigit(digit);
}
}
}
}
}
}
}