Reading Candidate Counts in Sudoku to Guide Your Next Move

Why reading candidate counts sudoku players win time

Reading candidate counts sudoku style means treating the size of each candidate list as a signpost. A cell with one candidate is a naked single you can fill immediately. A cell with two candidates is a bivalue cell, the raw material for naked pairs, X-Wings and chains. Cells crowded with five or six candidates are noise for now and best left alone. The same idea applies to units: if a value has only one legal cell in a row, column or box, it is a hidden single. Counting first tells you where the easy wins and the powerful patterns are hiding, so you spend effort only where it can pay off.

Low counts first, always

The practical rule is to work from low counts upward. After pencilling candidates, sweep for cells showing a single mark and place them, then look for cells showing two, because those feed nearly every intermediate technique. Compare r4c4 holding 2 and 9 with r4c5 holding 1, 2, 5, 7 and 9; the bivalue r4c4 is where your attention belongs, since it can pair, link or chain, while the crowded cell will resolve on its own once its neighbors settle. Reading counts stops you from wasting effort on cells that are simply not ready to be solved, which keeps your solving rhythm smooth.

Counting inside a unit

Counts matter for units as much as for cells. Scan a row and tally how many cells can still hold a given value. If a value has exactly one home, place it as a hidden single. If it has exactly two, you have a conjugate pair, a strong link that powers X-Wings and chains, so it is worth noting even when you cannot use it yet. For example, if the digit 7 in column c2 can only sit at r1c2 and r5c2, that two-count is a strong link between them. Reading these small numbers turns a static grid into a map of your next several moves.

• Fill every one-candidate cell before anything else.
• Collect two-candidate cells as fuel for pairs, fish and chains.
• Ignore cells crammed with five or more candidates for now.
• Count each value per unit; a count of one is a hidden single.
• Flag values with a count of two as strong links for later.

Keeping counts honest in Shapedoku

Accurate counts depend on accurate notes, and this is where Shapedoku helps most. Notes with smart cleanup removes candidates that can no longer be true, so the numbers you read reflect the real position instead of stale guesses. Because candidates appear as small shapes, a bivalue cell is easy to recognize by its two colors, and a value with only one home in a unit stands out fast. The free solver on shapedoku.com displays candidate counts and shows which move they justify, and if you want a nudge, the first Hint is free and explains why a shape fits. Mystic Sort from the studio SnailPixel is a calm companion puzzle, and app.shapedoku.com is always ready when you want to practise.