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📋 Last Possible Number – Sudoku Technique

When a cell, after row/column/box constraints, has only one candidate left, place that digit. Illustrated example.

What Is the Last Possible Number?

The last possible number technique looks at a single cell. If row, column and 3×3 box constraints eliminate all candidates but one, that digit must go there.

Step-by-Step Example

Step 1: Target cell; eliminate by row/column/box
1) The row already has 1, 9, 3, 4; the column has 2, 8, 7, 5. Only 6 remains possible.
Step 2: Single remaining candidate 6
2) The only candidate is 6 ⇒ place it.

Tips

  • Always check all three units of the cell (row, column, box).
  • Great for early progress when many cells are still empty.
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