Hard sudoku
Hard sudoku is where notes become essential, and the first patterns appear: digits locked into one line of a box, and cells that share the same two digits.
A thousand Hard puzzles, free in your browser. No sign-up, nothing to download.
What it takes
How often each technique is needed in the game’s Hard puzzles, counted over 300 of them:
- Hidden singlesin 100% of them
- Locked candidatesin 98% of them
- Pairsin 87% of them
- Naked singlesin 81% of them
Hard puzzles start with 26 to 30 digits given, 27 on average. Every one has exactly one solution, and none needs a guess.
Tips
- Fill in notes for the whole board before you look for patterns.
- Check each box for a digit that is stuck on one row or column.
- Two cells in a unit with the same two notes: those digits go from everywhere else in it.
Other levels
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