Quadruple Sudoku Help
Quadruple adds circle with up to 4 numbers. Those numbers must appear in one of the four cells surrounding the circle.
On image above we can see one quadruple with values 1, 2, 3 and 4. Since all quadruple cells are in same house (box 1), those cells must have 1, 2, 3 and 4 and no other cells in the house can have these digits.
Quadruple Sudoku Solving Strategies
On image above we can see quadruple with three digits where all quadruple cells are in the same house (box 1). This means we can rule out 1, 2 and 3 from other cells in box 1, but we cannot rule out any candidate from the four cells in quadruple because fourth digit is unknown.
When there is a value that can resolve fourth digit we can determine candidates. See image below.
Quadruple can have repeated digits if it is located in more than one box.
On image above 1 goes into either green cells or blue cells. 1s have to be placed diagonally. If we can rule out one of the 1s, we can place them both, as on image below (1 is rule out from green cell with greater than constraint).
When two quadruple are overlapping if they share a single cell we can determine digit of that cell in case all quadruple cells are in same house (box, or windoku window).
On image below common cell has to be 2 since it's required in both quadruples.
In case of overlapping quadruples where two cells are shared, those two cells must be in both quadruples. On image below we can se that common cells are 2 and 5, upper quadruple also has 8 and 9, and lower quadruple has 1 and 4. All those candidates can be removed from other cells in the box.
