Sudoku for beginners: find what is missing
Sudoku is not an arithmetic exercise. It is a placement problem: where a number can go, and where it cannot.
2 min · RafaGonMar · October 20, 2026
Three rules on one board
Every row, column and 3 × 3 box must contain each number from 1 to 9 exactly once. A number already in a row rules out every other cell in that row for that number. The same applies to columns and boxes.
Start with fewer possibilities
If a row is missing only two numbers, write them down and check the columns crossing the empty cells. You do not need to analyze the entire board to find your first step.
Look for a number, not just a cell
Try choosing one digit and scanning boxes. If two rows in a box are ruled out because that digit already appears outside the box, perhaps only one cell remains possible. A cell may have several candidates while still being the only place for a particular digit in its box.
Pencil marks work when maintained
Use Notes to record candidates without committing to an answer. After placing a digit, review notes in related cells. Outdated notes can be as misleading as an incorrect entry.
Checking is different from solving
Check marks entries that disagree with the solution. Hint fills a cell to help you continue, and Undo restores an earlier state. Every puzzle is checked for exactly one solution. Difficulty changes the clue count; it is not a formal rating based on required techniques.