Easy Killer Sudoku

About Easy Killer Sudoku

Easy killer sudoku: mostly small two- and three-cell cages, and a few single cells to get you going. Cage combinations and the simple 45 rule are all you need.

Killer Sudoku is sudoku with sums instead of starting digits. The grid is split into cages, drawn with dotted outlines, and the small number in each cage’s corner is what its digits add up to. Fill every row, column and 3×3 box with 1 to 9, make every cage add up, and never repeat a digit inside a cage. Every puzzle here has exactly one solution, reachable by logic.

Also called: sum sudoku, samunamupure.

How to play Killer Sudoku

1. Select a cell by tapping or clicking it, or move around with the arrow keys. Its row, column and box turn cream, and the rest of its cage is tinted.
2. Enter a digit with the number pad or the keys 1–9. Enter the same digit again, or press Backspace, to clear it.
3. Under the pad, the cage helper lists every set of different digits that makes the selected cage’s sum, such as 1 5 9 or 2 4 9 for 15 in three cells. Sets that no longer fit the digits you have already placed in the cage are crossed out.
4. Turn on Notes (the pencil, or press N) to pencil small candidates into a cell. Shift plus a digit adds a note without switching modes. Placing a digit removes it from the notes in its row, column, box and cage.
5. Undo and Redo (Ctrl+Z and Ctrl+Y) as often as you like. Hint fills one correct cell, the one logic says comes next, and tells you why.
6. A digit that repeats in a row, column, box or cage turns red, and a cage sum turns red when the digits in it go over the total or fill it with the wrong total. For more help, switch on Check answers to mark every wrong digit. It’s an assist, like a hint: the puzzle still counts, but it can’t set a best time.

Rules

• Each row, each column and each 3×3 box contains the digits 1–9 once each, just as in sudoku.
• The digits in each cage add up to the number in its corner.
• A digit can’t appear twice in the same cage, even when the cage spans more than one box.
• There are no starting digits: the cage sums are all the clues you get.
• The puzzle is solved when every cell is filled and every rule holds. Solves with hints or Check answers count as wins but don’t set a best time.

Killer Sudoku tips and strategy

• Start with the tight cages. Some sums can only be made one way: 3 in two cells is always 1 and 2, 4 in two is 1 and 3, 17 in two is 8 and 9, 6 in three is 1 2 3, and 24 in three is 7 8 9.
• Use the 45 rule. Every row, column and box adds up to 45. Add up the cages that sit entirely inside a box; the cells left over (the “innies”) must make up the difference. It works for cages that poke out of a region too: the cells outside it (the “outies”) make the excess.
• Look at runs of rows or columns. The 45 rule also works on two or three rows together (90 and 135), which often exposes a single cell.
• A digit a cage must use goes somewhere in it. If every way of making a cage’s sum uses a 9, and the cage sits inside one row, no other cell of that row can be a 9.
• Mix in plain sudoku. Once a few digits are in, the usual singles, pairs and pointing work as normal. Harder puzzles need hidden pairs and triples too.