Full House / Last Digit Sudoku

What Full House means

A Full House is a row, column, or 3x3 box where all cells are filled except one. The empty cell is forced because every house must contain the digits 1 to 9 exactly once.

This technique is also called Last Digit. It is easy to recognize, safe to solve, and usually the first technique beginners should scan for.

Box example: find the last digit

Start with the highlighted box. It has only one empty cell: R7C2.

All the other cells in this box are filled and contain every digit from 1 to 9 except 7.

Walk through this in steps 1-3 of the guided example above

Row example: Full House is not only for boxes

A Full House can appear in any house: a row, a column, or a box.

In this row example, row 6 has one empty cell, R6C4. The only digit missing from row 6 is 8, so the empty cell must be 8.

Walk through this in steps 4-5 of the guided example above

How to use Full House while solving

Full House is most useful at the start of easy puzzles and after another move fills a house to eight cells. One placement often creates the next Full House nearby.

1. Scan boxes, rows, and columns that are almost complete.
2. Count which digit from 1 to 9 is missing.
3. Check that the empty cell belongs to that house.
4. Place the missing digit only when there is exactly one empty cell.
5. After placing it, scan the affected row, column, and box again.