SudokuBoku

Easy sudoku

Forty clues, and a promise: you will never need anything cleverer than looking at a square and seeing that eight of the nine digits are already spoken for.

Easy Medium Hard Expert Evil Extreme

00:00 Mistakes 0
Puzzle —
Rules
  • Fill every row, every column and every 3×3 box with the digits 1 to 9.
  • A digit can appear once in each of those — never twice.
  • There is exactly one solution, and logic alone will reach it.
  • Rows and columns each take the digits 1 to 9, once apiece.
  • The boxes are irregular shapes, drawn with the heavy outlines.
  • However a region bends, no digit repeats inside it.
  • The colour patches are cages; the small number is what a cage's digits add up to.
  • No digit repeats within a cage — nor in any row, column or 3×3 box.
  • There are no given digits: the sums alone pin down the whole grid.
  • Everything from classic applies: rows, columns and 3×3 boxes take 1 to 9.
  • The two tinted diagonals must each hold 1 to 9 exactly once as well.
  • All the classic constraints hold — rows, columns and 3×3 boxes take 1 to 9.
  • Each of the four shaded windows must also contain 1 to 9 exactly once.
  • The windows sit a step in from the corners, overlapping four boxes apiece.
  • Rows, columns and 3×3 boxes work exactly as they always have.
  • On top of that, two squares a chess knight's move apart may not hold the same digit.
  • Select a square and its knight partners are ringed with a dashed outline.
  • Every row, column and 3×3 box holds 1 to 9, exactly as in classic.
  • Along each grey path, digits strictly climb from the round bulb to the far end.
  • They don't have to be consecutive — each square just beats the one before it.
  • Rows, columns and 3×3 boxes take 1 to 9, exactly as in classic.
  • The digits along each arrow add up to the digit in the circle it comes from.
  • Digits may repeat along an arrow — as long as no row, column or box objects.
  • Fill every row, column and 3×3 box with the digits 1 to 9, as usual.
  • Between squares in the same box you'll find a sign; its point aims at the smaller digit.
  • Every comparison inside every box is shown — a hundred and eight of them.
  • The higher levels hand you fewer digits, not fewer signs. Expert gives you four.
  • Fill every row, column and 3×3 box with the digits 1 to 9, as usual.
  • A white dot between two squares means their digits differ by one.
  • A black dot means one digit is exactly double the other. 1 and 2 are both, and always show black.
  • A boundary with no dot is a clue too — those two digits are neither one apart nor double and half. Every boundary is marked or deliberately bare.
  • Expert hands you no digits at all. The dots and the gaps are the whole puzzle.
  • Fill every row, column and 3×3 box with the digits 1 to 9, as usual.
  • A square with a ring behind it holds an odd digit — 1, 3, 5, 7 or 9.
  • A square with a frame behind it holds an even one — 2, 4, 6 or 8.
  • Most squares are marked with neither, and those are genuinely unrestricted.
  • Every square switches to the fully marked board — one level, gentler than it looks, and two puzzles sharing a grid rather than one.
  • Every row, column and box holds five odd digits and four even ones — so once five squares of a house are known odd, the rest of it is even, marked or not.
  • Solve the 9×9 sudoku as usual — every row, column and box takes 1 to 9.
  • Ten ships are hidden on the same squares: one of four, two of three, three of two and four single squares.
  • Ships are straight, and no two of them touch — not even at a corner.
  • The numbers beside and below say how many ship squares each row and column holds.
  • A ship listed with digits sits on exactly those digits, in order — so the grid is your map.
  • Five 9×9 grids interlock: four corners and a centre, each corner sharing one 3×3 box with it.
  • Every grid obeys ordinary sudoku on its own — rows, columns and boxes each take 1 to 9 once.
  • A tinted box belongs to two grids at once, and only together do the five have one solution.
  • Fill every row, every column and every box with the digits 1 to 6.
  • The boxes are three squares wide and two tall.
  • Nothing repeats in any row, column or box.
  • Put 1, 2, 3 and 4 into each row, each column and each 2×2 box.
  • No digit may appear twice in any of them.
  • Every square can be worked out — no guessing needed.
Keyboard shortcuts
1–9
Place a digit, or toggle a pencil mark
Arrows
Move around the grid
N
Notes mode on or off
Backspace
Clear the square
Ctrl + Z
Undo · Ctrl + Y redo

What "easy" is guaranteeing

On most sites the easy label means "we left more numbers in". Here it means something you can hold us to. Before an easy puzzle reaches your screen it is solved by a program that works the way a person does, and it only earns the label if the entire grid falls to naked singles — squares where eight of the nine digits are already used up by the row, column and box, leaving exactly one possibility.

Nothing else is required. Not pencil marks, not pairs, and certainly not guessing. If you ever find yourself stuck on an easy grid here, you haven't hit a wall — you've missed a square, and there is definitely one sitting there waiting.

The whole technique, in one move

Pick an empty square. Ask three questions:

  1. Which digits are already in its row?
  2. Which are in its column?
  3. Which are in its three-by-three box?

Cross all of those off your mental list of 1 to 9. On an easy puzzle, you will regularly find one digit left standing. Write it in. That single placement changes the answer for every square that shares a row, column or box with it, which is why easy grids tend to unravel in bursts — one placement makes the next one visible.

From the tinted square, eight digits are already in view — three along its row, three down its column, two more in its box. Only a 9 is left, and that is the entire move.

Where to look first

Don't sweep left to right. Start with whichever three-by-three box already has the most digits in it, because a box holding six or seven numbers has very little freedom left. Work that box until it stops giving, then move to whichever box now looks fullest. You'll finish a grid noticeably faster than you would reading it like a page.

Easy puzzles are not a waste of your time

There's a tendency to treat easy as the level you graduate from. Three reasons to keep one in rotation:

They build the scan you'll need later. Every harder technique sits on top of the ability to look at a square and know instantly what can't go there. On an easy grid you practise that hundreds of times without the interference of pencil marks.

They're the honest speed test. Because the technique never varies, your time is a clean measure of how quickly you scan — not how lucky you were with a pattern. Solve a few and watch the clock come down.

They're the right level to teach with. If you're introducing sudoku to someone, an easy grid lets you explain the whole game in one sentence and then let them find placements unaided within a minute. Anything harder means teaching bookkeeping before they've enjoyed the puzzle.

Knowing when to move up

The signal isn't speed, it's boredom of a particular kind — when you stop searching for the next square and start simply seeing it. At that point the puzzle has become transcription rather than deduction, and it's time for medium, where you'll have to start asking where a digit can go rather than what fits in a square. It's a small shift in perspective and it opens up most of the rest of sudoku.