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Daily Killer Sudoku (Hard)
Wednesday 8th July 2015
Killer Sudoku leaderboard
How to play
This is an example of a completed Killer Sudoku puzzle. The grid is split up in to cages; each cage
contains 2 or more cells, and has a total in the top-left corner. The cells in each cage must
add up to the given total.
As an example, the cage in the top-left of this puzzle contains three cells, and they must add up to 17.
We can check, and 3+8+6 does give 17.
Killer Sudoku puzzle are much harder than normal Sudoku puzzles, you should be able to comfortably solve
a difficult Sudoku puzzle before trying to solve a Killer Sudoku puzzle.
This is a Killer Sudoku starting grid, the first thing you'll need notice is that there are no starting
numbers! We need to use a different set of techniques to get started with Killer Sudoku puzzles. We know
that each row column and 3x3 region will contain the numbers 1-9, if we add these together we get
1+2+3+4+5+6+7+8+9=45, i.e. each row, column, and 3x3 region must add to 45/
Look at the bottom-right 3x3 region, we have 4 cages that add to 16+7+10+4=37. These cages between them
cover 8 out of the 9 cells in this region. That means the remaining (highlighted) cell must be 45-37=8.
This is a great technique to use when starting with Killer Sudoku grids. You will also use techniques
that you might use for Mathdoku puzzles. For example, the cage with 2 cells adding to 4 in the bottom-right
only has one combination, i.e. 1+3=4. We can pencil these in and use the naked pairs technique.
This is another example Killer Sudoku starting grid. We can't use the same technique for this grid, but we
can use something very similar. Consider the two right-most columns, we know these cells must add to
90, i.e. 2x45. All but two of the cells (the highlighted ones) in these two columns are contained in a set of
cages, and these cages don't cross in to the adjacent column. Adding these cage totals up gives
13+8+14+8+10+16+9=78. That means the two highlighted cells must add up to 90-78=12, this gives us a little
more information about those cells than we had previously!
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There are two ways to play a Sudoku puzzle, you can just use the mouse/touchscreen, or you can use the mouse and keyboard.
You can switch between the two methods any time you like, and can use a combination of both.
Playing with a mouse/touchscreen.
- When you have found a square where you can enter a number, click/touch that square. The square will turn light blue.
Above and below the puzzle is the number selection. Click/touch the number you want to enter in to that cell.
If there is already a number in that square, it will be over-written.
- If you want to enter a pencil mark, click/touch the square you want to put in a pencil mark. It will turn light blue.
Click/touch the pencil icon above or below the puzzle. This icon will turn light blue, and you are now in pencil marks mode.
Whenever you click/touch a number now, a pencil mark will be put in the square instead.
To remove a number as a pencil mark, make sure you are in pencil marks mode, and click/touch the number again.
You can exit pencil mark mode by clicking/touching the pencil icon, it will turn back to normal.
- If you want to clear a particular square, make sure that square is selected and is in light blue.
Click/touch the eraser icon. If there is a number in that square, it will be removed.
If you click/touch it again, any pencil marks in that square will be removed.
Playing with a mouse and keyboard.
- You will need to select a square by clicking on it with the mouse, it will turn light blue.
You can change the current square by using the cursor keys on your keyboard.
- To enter a number, press that number on the keyboard. If there is already a number in that square, it will be overwritten.
To remove a number, press the backspace or delete key on your keyboard.
- To enter a pencil mark, press control, shift, or alt on your keyboard at the same time as pressing a number key.
Do the same thing again to remove that pencil mark.
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