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Killer Sudoku Help

Rules / Objectives Summary

  • Every square contains a number.
  • Complete the grid such that every row, every column, and every 3 x 3 block contains the digits from 1 to 9.
  • Every square belongs to a cage, and every cage has a little number in its corner. The number is the sum of the digits in the cage.
  • A number cannot appear more than once in a cage (which is different to CalcuDoku).

See the Basic Ideas, Advanced Ideas and the Walkthrough for extra tips and tricks, and don't forget that underneath everything, these are Sudoku puzzles, and all of the information in the Sudoku help can help you as well.

Killer Sudoku Puzzle


What are the numbers for?
These tell you the sums of the digits in each cage, where a cage is a collection of two or more squares inside a dotted enclosure.

Move your mouse over the puzzle to see the answer.



Basic Ideas

  • Normal Sudoku rules, tips, tricks and techniques apply. Click here for the Sudoku help page.
  • Every row, column, and 3 x 3 block must contain the digits 1 to 9.
  • The puzzle is broken down into cages, and the small number in the corner tells you the sum of the digits in a cage, 9 = 6 + 2 + 1.
  • Pencil marks are the easiest way of keeping track of possible values for each square. Here we see the cage clue of 4, which can only be 1+3 or 3+1, so we enter both numbers into the squares.
  • We can use pencil marks to enter possible values for all of our cages. Cages such as 5 can't have the larger numbers. And notice how 6 cannot be 3 + 3 as we are not allowed duplicate numbers within a cage.
  • We can also use the Kakuro Combinations to reduce the number possible values for some cages, for example a two square cage of 16 can only be <79> in some order.


Advanced Ideas

  • As we have to have 1 to 9 in each 3 x 3 Block, the digits within each Block must add to 45 (1 + 2 + 3 + ... + 9). Notice how these cages also add to 45 (11 + 8 + 9 + 17), as they are all fully contained within the Block.
  • Knowing that the Block adds to 45 can help us to make a start on many Killer Sudoku. Here we can see that four cages are entirely within the Block, and they add to 42 (7 + 17 + 7 + 11). This means that the other square in the Block is <3>, to make 45.
  • Here is another great starter for many Killer Sudoku. Here we can see four cages that are almost within a single Block and they add to 50 (22 + 8 + 11 + 9). We know that the Block adds to 45, so the remaining <5> must be outside the Block, but inside the cage.
  • Both of these techniques can be applied to Rows and Columns as well. Here we have four cages that add to 40 (5 + 13 + 17 + 5), so the remaining <5> must go in the first square.
  • We know that the 3 cage must contain <12>, in some order. Therefore we also know that the <1> and the <2> CANNOT appear anywhere else in this Row. This technique can be applied to Rows, Columns and Blocks.


Walkthrough

Help 1



Step 1
This is the start of the puzzle.

Solve this puzzle for yourself at the same time.

Help 2



Step 2
We can use the fact that we've four cages entirely within the block, and they add to 39 (9 + 7 + 17 + 6), which makes the other square <6> (so they add to 45).

Help 3



Step 3
The other square in the 15 cage must therefore be <9>.

Help 4



Step 4
This is the only cage where the <9> can go (the other cages clues are smaller than 9), and as the clue is 17 the other number must be <8>.

Help 5



Step 5
Where can the <1> go?. Well it can't go in the 9 cage as we'd need a <8> to go with it, but we know where the <8> is. It can't go in the 7 cage as we'd need a <6> to go with it, and we know where the <6> is. So it must go here, and the other number in the cage must be <5>.

Help 6



Step 6
Where can the <2> go? Similarly, it can't go in the 7 cage as we'd need a <5> to go with it, but we know where the <5> is, so the <2> must go in the 9 cage along with the <7>.

Help 7



Step 7
Which leaves the <3> and <4> to go in the 7 cage, which starts this little section off nicely ready for the rest of the solution to eliminate some more numbers.


 

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