Puzzle Terms: A Small Reference for Your Next Move

NewGames.ai · https://newgames.ai/puzzle-terms/

A familiar word can mean something quite specific in a puzzle. This reference explains the terms used in our learning guides and points to an example for each check. Start with the word you need; there is no need to read the whole page before returning to your board.

The Sudoku definitions refer to classic Sudoku. The block definitions describe our fixed teaching exercises, not every game’s rules or controls.

Cell, Row, Column And Box

A cell is one square. A row runs across the board; a column runs down it. In classic Sudoku, a box is one of the nine 3-by-3 regions. Each row, column and box needs the digits 1 through 9 without repetition. These are the groups described in Nikoli’s standard rules.

A position label is not a number to enter. “Column 5” identifies the fifth column from the left. In our block exercises, C2 means column C, row 2. Read the table’s labels before interpreting its contents.

Review the three Sudoku groups.

Candidate

A candidate is a digit not yet ruled out for an empty Sudoku cell by the checks you have made. It is a possibility, not a confirmed entry. In our practice tables, each list includes every digit allowed by that cell’s current row, column and box.

Writing “2, 3” means that both remain possible under those checks. It does not mean that either is safe to enter. On your own board, incomplete or outdated notes can hide a possibility, so recheck the groups before relying on them.

Follow candidates through three checks.

One Candidate In A Cell

After checking all three groups, just one candidate may remain in a cell. With correct clues and entries, that gives a reason to place the digit. The key is what you have ruled out, not which number looks promising.

Do not confuse one note you happened to write with a complete list containing one candidate.

Try the one-candidate example.

One Place For A Digit

This reverses the question: instead of counting digits in one cell, count the possible cells for one missing digit within a group. If only one location allows it, the digit belongs there, even if that cell has other candidates. This is the hidden single described in Sudoku.com’s explanation.

Check every empty cell in the group. A digit appearing only once in incomplete notes is not enough evidence.

Compare one location with two possible locations.

Contradiction

A contradiction means the information you are relying on cannot all be right under the rules. Examples include an empty Sudoku cell with no allowed digit, or a row missing a digit with nowhere to put it.

This is a reason to recheck, not permission to guess. Review the clues, your entries and the exclusions in your notes. Empty notes alone do not prove a contradiction if you have not completed the checks.

Work through a conflicting-notes example.

Piece Footprint

A block piece’s footprint is the full set of cells it would cover. Every part must fit, not just the first square. In our exercises, a legal placement stays inside the board, covers only empty cells and does not rotate the supplied shape.

Two empty cells separated by an occupied cell cannot hold one horizontal two-cell piece.

Check a complete piece’s fit.

Line Clear

In our block exercises, a line clear removes a completely filled row or column after placement. Identify all completed lines on the same board before removing them; the clears happen together. The remaining blocks do not fall.

Those are the rules for these examples. A different game may clear shapes differently, so consult its instructions rather than assuming the same behavior.

Compare the boards before and after a clear.

Usable Space

Usable space means room for a particular piece’s whole footprint. It is not simply the total number of empty cells. A 2-by-2 square needs two adjacent empty cells in each of two adjacent rows; four scattered gaps are not equivalent.

When the next piece is known, check its shape against the board that will remain after the current move and any clears.

Compare two placements and the space left behind.

Return Note

A return note is our name for a short reminder of what you know, what is unresolved and what you plan to check next. It can help you resume your reasoning, but it does not save or restore a game’s board.

If the position has changed, check it again before following an old note.

Use the return checklist, or choose a practice example.