Extreme Killer Sudoku
Hard killer sudoku puzzles
A killer sudoku gives you no digits at all, only cages and their totals. Easy killers open up after a few obvious cages. Hard ones keep you working with the 45 rule, cage combinations and the same wings and chains as an expert sudoku, all the way to the end.
What makes a killer sudoku hard
Small cages with extreme totals (3 in two cells, 24 in three) are gifts. Hard killers have few of them, and big cages whose combinations only narrow down when you combine them with rows, columns and boxes.
Our grade is set by the hardest technique a solver must use and by how many times the solve gets stuck at that level. A grid that is easy except for one clever step does not make the cut.
Every grid has exactly one solution and can be solved by logic alone. You never have to guess.
Our killer books use our top levels only, Expert 2 and above. Expert 2 already needs innies, outies and cage splitting together with sudoku patterns; Expert 4 and 5 need chains on top.
The techniques you will need
These are the advanced and expert techniques that come up most often in our killer sudoku walkthroughs. Each link explains the idea in plain words and shows it in real puzzles.
- Forcing Chains in 436 walkthroughs
- Try each candidate of one cell in turn. Every choice leads to the same result, so that result must be true.
- Multi-Sector Locking in 346 walkthroughs
- A digit the cage must contain can only go in one row, column or box, so it is ruled out of the rest of that row, column or box (or the other way round).
- Advanced Innies (3+ sectors) in 345 walkthroughs
- The 45 rule over three or four rows or columns at once fixes a cell or the total of a small group of cells.
- Coloring/Multi-coloring in 279 walkthroughs
- Following one digit’s strong links, cells get two colours: one colour is true and the other is false. A cell that sees both colours cannot hold the digit.
- Remote Pairs in 221 walkthroughs
- A chain of cells that all hold the same pair alternates between the two digits. Cells that see both ends of an odd-length link cannot hold either digit.
- Finned Fish in 108 walkthroughs
- An X-Wing or Swordfish with one extra candidate (the fin). Cells that are in the fish pattern and also see the fin lose the digit.
- Empty Rectangle in 104 walkthroughs
- In one box a digit is confined to an L or cross shape. Combined with a strong link outside the box, it rules the digit out of one cell.
- 2-String Kite in 88 walkthroughs
- A row and a column each have a digit in exactly two places, linked through one box. One of the two far ends holds the digit, so a cell seeing both ends cannot.
The full ladder, from naked singles up: killer sudoku techniques.
How to get better at hard killer sudoku
- Start with the 45 rule everywhere: every row, column and box adds up to 45. Innies and outies give you totals for cells no cage tells you about.
- Learn the fixed combinations: 3 = 1+2, 4 = 1+3, 16 = 7+9, 17 = 8+9 in two cells; 6 = 1+2+3 and 24 = 7+8+9 in three.
- Write the possible combinations of each big cage beside it, and cross them out as digits are placed. Most hard steps come from a cage running out of options.
- Once the cages stop giving, switch to pencil marks and look for the ordinary sudoku patterns: pairs, X-Wings, wings.
The toughest killer sudoku puzzles in our books
Ranked by level, then by how many times the solve needs an advanced or expert step. Each has a free step-by-step solution: try the puzzle from the book first, then check where you got stuck.
- Extreme Killer Sudoku 3, puzzle 9 Expert 4 · 14 hard steps · key technique Remote Pairs
- Extreme Killer Sudoku 3, puzzle 100 Expert 4 · 13 hard steps · key technique Coloring/Multi-coloring
- Extreme Killer Sudoku 2, puzzle 121 Expert 4 · 12 hard steps · key technique Coloring/Multi-coloring
- Extreme Killer Sudoku 1, puzzle 126 Expert 4 · 11 hard steps · key technique Coloring/Multi-coloring
- Extreme Killer Sudoku 1, puzzle 10 Expert 4 · 9 hard steps · key technique Finned Fish
- Extreme Killer Sudoku 1, puzzle 141 Expert 4 · 9 hard steps · key technique Coloring/Multi-coloring
- Extreme Killer Sudoku 2, puzzle 111 Expert 4 · 9 hard steps · key technique Coloring/Multi-coloring
- Extreme Killer Sudoku 3, puzzle 8 Expert 4 · 9 hard steps · key technique Coloring/Multi-coloring
- Extreme Killer Sudoku 3, puzzle 10 Expert 4 · 9 hard steps · key technique Remote Pairs
- Extreme Killer Sudoku 3, puzzle 41 Expert 4 · 9 hard steps · key technique Remote Pairs
- Extreme Killer Sudoku 1, puzzle 6 Expert 4 · 7 hard steps · key technique Coloring/Multi-coloring
- Extreme Killer Sudoku 3, puzzle 21 Expert 4 · 7 hard steps · key technique Coloring/Multi-coloring
The books
Each book has 150 puzzles, one per page, ordered from the easiest to the hardest, with full solutions at the back and a QR code beside every solution that opens its step-by-step walkthrough. £9.99 / $11.99.
| Book | Expert 4 | Expert 3 | Expert 2 | Solutions |
|---|---|---|---|---|
| Extreme Killer Sudoku 1 | 5 | 37 | 108 | all 150 |
| Extreme Killer Sudoku 2 | 2 | 27 | 121 | all 150 |
| Extreme Killer Sudoku 3 | 8 | 50 | 92 | all 150 |
Those buttons open Extreme Killer Sudoku 1; each book has its own page above.
Try one free
Every book has a free printable sample puzzle with its own step-by-step solution: see free puzzles. Prefer classic grids? Try hard sudoku. Or something with letters: the five-letter wordsearch.