Killer Sudoku Game and Solver: Play Killer Sudoku Online, Free
Play killer sudoku online, free: sudoku's rules plus cages, groups of cells whose digits add up to a sum. Easy, medium, hard or expert, with notes and hints. Stuck on one from a paper or an app? Draw its cages in the killer sudoku solver and watch it filled, cell by cell.
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- Each row, each column and each 3 × 3 box holds the numbers 1 to 9, each once, as in sudoku.
- The grid is cut into cages, drawn with dashed lines, each with a sum in its corner.
- The digits of a cage add up to its sum.
- A digit never repeats inside a cage.
Easy, medium, hard and expert killer sudoku
Every puzzle here has one solution. The fewer and bigger the cages, the more ways each sum can be made, and the harder it gets:
- Easyabout 40 cages, mostly of 2 cells, a dozen more digits given, and every cell found without guessing
- Mediumabout 31 cages of 2 to 4 cells, and five more digits given
- Hardabout 27 cages, mostly of 3 and 4 cells, and no digits given but the cages of one cell
- Expertabout 25 cages, many of 4 and 5 cells; notes and the 45 rule all the way
How to solve killer sudoku: four techniques
Cages with one way
Some sums can be made only one way: a cage of two cells adding up to 3 holds 1 and 2, whatever else is around it. Start with those cages, and the cages of one cell, which give their digit away.
The 45 rule
Each row, column and box adds up to 45. Add the cages that lie wholly inside a box: what is missing from 45 is the sum of the box's other cells. One cell sticking out of a box gives its value the same way.
Notes of combinations
For a cage of 17 in two cells, only 8 and 9 fit. Write those in small. Every digit you place crosses itself out of its row, column, box and cage.
Sudoku's own ways
Everything that works in sudoku works here: the only number left for a cell, the only place left for a number in a row, column or box, and pairs.
Stuck? Press Hint on the game: it shows the next cell to fill and why, from wherever the grid stands.
Killer sudoku combinations with one way
These cage sums can be made by one set of digits only, so the cage's digits are known at once; only their order is left:
- 3 = 1 + 2
- 4 = 1 + 3
- 16 = 7 + 9
- 17 = 8 + 9
- 6 = 1 + 2 + 3
- 7 = 1 + 2 + 4
- 23 = 6 + 8 + 9
- 24 = 7 + 8 + 9
- 10 = 1 + 2 + 3 + 4
- 11 = 1 + 2 + 3 + 5
- 29 = 5 + 7 + 8 + 9
- 30 = 6 + 7 + 8 + 9
How the killer sudoku solver works
It checks your cages first: every cell in a cage, each sum possible for its cage's size, and all sums adding up to 405. Then it fills the grid the way a person would: the only number left for a cell, the only place left for a number in a row, column or box, or the only cell of a cage that can take a digit the cage must hold. When nothing is certain, it takes the cell with the fewest numbers left. It also says when the cages allow no solution, or more than one.
Where killer sudoku comes from
In Japan the puzzle ran in the 1990s as samunamupure, "sum number place", a mix of sudoku and the sums of kakuro. The Times in London, which had started printing sudoku in 2004, brought it to Britain in 2005 as killer sudoku, and other papers followed.
Questions
How do you play killer sudoku?
Fill the 9 × 9 grid so that each row, column and 3 × 3 box holds 1 to 9 once, as in sudoku. The grid is also cut into cages drawn with dashed lines: the digits of a cage add up to the small number in its corner and never repeat inside it.
What is the 45 rule in killer sudoku?
Each row, column and box holds 1 to 9, which add up to 45. So the cells of a box add up to 45, and the sum of a few of them is 45 minus the cages that cover the rest. It is the strongest tool in killer sudoku.
Can a number repeat in a killer sudoku cage?
No. A digit is never twice in one cage, even when the cage runs across two boxes.
Does killer sudoku have given numbers?
A classic one has none: the cages and their sums are the clues. Here a cage of a single cell shows its digit, since its sum is that digit; easy puzzles start with a dozen more digits filled in and medium ones with five, hard and expert with none.
What do all the cage sums add up to?
Every cage sum together comes to 405, nine rows of 45. The solver checks this before it starts: a sum typed wrong shows there.
How do I solve my own killer sudoku?
In the solver above, drag across the cells of one cage (or tap them one by one) and type its sum; do every cage the same way. Then press Solve. It fills the grid one cell at a time and says why each number goes where it goes.
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