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Sudoku Xtra, written by Dr Gareth Moore
Sudoku Xtra 24
logic puzzle compendium
Printed puzzles from Dr Gareth Moore

Sudoku
 
Hanjie
 
Kakuro
 
Futoshiki
 
Calcudoku
 
Hitori
 
Killer Sudoku
 
Nurikabe
 
Slitherlink
 
Skyscraper

Sudoku-X
 
Jigsaw Sudoku
 
Consecutive Sudoku
 
Kropki Sudoku
 
Sudoku XV
 
Oddpair Sudoku
 
Toroidal Sudoku
 
Killer Sudoku-X
 
Killer Sudoku
Pro

 
Jigsaw Killer
Sudoku

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How to play Calcudoku

Calcudoku combines the row and column constraints of Sudoku with numerical regions that are similar - but not identical - to those in Killer Sudoku.

To solve Calcudoku, place the numbers 1 to 6 (or whatever the width of the puzzle is) once each into every row and every column. Further, the given value at the top-left of each bold-lined region must be obtained when all of the numbers in that region have the given operation (+, -, ×, ÷) applied between them. For - and ÷ operations start with the largest number in the region and then subtract or divide by the other numbers.

In Mystery Calcudoku a '?' is given instead of an operation. In these you must work out the operation too - at least one of adding, subtracting, multiply or dividing results in the given total.

Note that there is no constraint on repeating numbers in bold-lined regions - calcudoku is different to jigsaw sudoku and killer sudoku puzzle in this respect.

To help understand the fundamental rules, consider the "1-" region at the top-left of the puzzle below. The two numbers in this region must result in 1 when the "-" operation is applied between them, with the smaller number subtracted from the larger. Therefore possible solutions to this region are 1 and 2 (since 2-1=1), or alternatively 2 and 3, or 3 and 4, or 4 and 5, or finally 5 and 6, and these could be written in either order into the two cells.

We can start solving this puzzle by writing in a few of the possible solutions to the numeric regions, beginning with some of those which have only one possible pair of digits. For example the "20×" in the top row can only be solved by 4 and 5 (4×5=20):

Note the cell in green. There must already be a 4 and 6 in this column, and since numbers cannot be repeated in a column we know this must be a 5. This also means there is only one solution to the 9+ region at the bottom-right now:

Because we must have each number from 1 to the size of the puzzle (6 in this case) in each row and column, we now know that the top-right-most cell in the grid must be a 1. This in turn lets us complete the 3÷ region that this 1 is now in with a 3, since 3÷1=3, and we also now can narrow the 2 and 6 in the top row down to two possible cells:

Notice how the green cell has three possible options to the two above it. This is because the possible solutions involving the 2 and 6 we have already placed are 6-5=1, 2-1=1 and 3-2=1 - i.e. the 1, 3 and 5 that are now options in that cell.

We can make several more deductions in a similar fashion, for example that the 2× in the bottom row must be solved by 1 and 2, and the elimination of the 3 from the right-most cell in the 3× region now that we have a 3 in that column already:

The cell marked in green is part of a 2- region. To use the 5 candidate the solution would need to be 5-3, but the 3 would share a row with an already-placed 3, so the solution must be 4. This in turn lets us complete more of the top row of the puzzle:

From here we need only make similar steps and soon we will have completed the entire puzzle:

Calcudoku makes use of many of the same tricks that you will use on Sudoku and Killer Sudoku, but don't forget that numbers can repeat in bold-lined regions. This means, for example, that a 6+ region of 3 cells could be solved by 1, 1 and 4 (so long as the region was L-shaped, otherwise the row or column constraint would prevent the repeat).

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