Killer puzzles

Unlike ordinary Sudoku puzzles, which can be solved purely with the aid of logic, killer puzzles involve arithmetic as well. The standard grid is partitioned into irregular shaped areas, outlined in grey with a number shown top-left. The digits placed in the area must add up to the number shown, and no digit may appear more than once in the same area. Finally the digits must obey the normal Sudoku constraints, so only one of each may appear in each column, row or square block.

To explain some of the techniques used in solving killer puzzles, please look at the example below of a 9×9 Killer.

Clearly we can put a 7 in the centre square of the puzzle.

Now look at the bottom-right square of the central block. It is part of an area of two squares which total sixteen. The only way to achieve this using the digits from 1 to 9 is to use a 7 and a 9, as we may not repeat two eights in the same area. The 7 cannot appear in the central block, as that already contains a 7 in the central square, so within the area concerned the nine appears on the left and the seven on the right.

The square top-left in the central block is one of two squares in an area totalling seventeen. The only digits that will work are 8 and 9. We have already placed a 9 in the central block, so the 8 must go in the top-left square of the central block with 9 to its left.

Often during the solution of a killer puzzle there will be more than one way to make up the total for an area. For example, the area of three squares totalling 21 in the top-right block could be 4+8+9, 5+7+9 or 6+7+8. As the puzzle progresses, these possibilities will be narrowed down as you fill in values in intersecting blocks, columns or rows.

SuperDoku's square analyser will ease some of the hard work by displaying not only the remaining possibilities for each square according to normal Sudoku rules, but also the combinations which are possible to achieve the required total for an area.

Creating puzzles

As an alternative to having SuperDoku generate a new killer puzzle for you, you can start from a blank grid and create a killer puzzle yourself or type one in from another source. Ensure that "Killer" is ticked in the puzzle creation window before you click on "Blank grid".

Editing consists of allocating squares to areas and entering the total value for each area. Click Select on an unallocated square to start defining a new area. Adjacent squares may be added to this area by clicking with Adjust. Squares within the current area may be removed by clicking with Adjust, providing that the remaining squares still form a contiguous area. You may also drag with Select or Adjust to create or alter areas. Click Select on an area you have already defined to select it in order to add or remove squares or change the total.

The totals for each area are shown at the top left. If the total is impossible to achieve in that number of squares it is displayed in red. To alter a total simply type the new number: there is no need to press delete.

When you have finished defining the killer puzzle, click the puzzle design editor tool to leave design mode. SuperDoku will check whether all squares have been allocated to groups and ensure that the totals are correct. You may then proceed to solve the puzzle, save it for the future, or to export it as a Draw file.

Note that it is possible to save or create Draw files of partially-defined killer puzzles while you are in design mode. If you load in such a puzzle you will be returned to design mode so that you can finish defining it. It is also possible to reenter design mode at any time while attempting to solve a puzzle, if you wish to adjust the puzzle's definition.


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