Solving every sudoku puzzle ends with the completion of three houses when you have that satisfying moment of entering the final digit! There are 27 houses in total to fill (though entering a number can create more than one full house at a time particularly towards the end of the puzzle) and completing a full house is the easiest technique to spot that you'll use every time you play! This is also a special case of a naked single.
The Full House occurs when 8 of the numbers from 1 to 9 are already present in any one house and the remaining digit is all that is needed to complete the full house. No need to scan rows or columns or check other cells - there is no doubt about it, assuming all the other numbers are correct. They come in three flavours: row, column and box.
Here we already have 8 numbers filling the 6th row which means there must be only 1 number remaining to complete the house, in this case a row. The number missing is 2.
This time we are one number short of completing the 6th column. We already know 8 of the numbers and a quick scan down the column for those that are already there quickly reveals that the number 4 is our missing digit
Now we have nearly completed a 3x3 box of 9 cells, with 8 of them already filled. We need just one more number to complete the Full House. Very quickly we can see that 9 goes in the last cell in the house. Box full houses tend to be much easier to spot than rows or columns as we find it easier to focus on one area at a time rather than a whole row or column. Most techniques are easier when they are confined to a single box rather than when spread out over the width of the whole grid.
The last digit to be entered into the final empty cell always completes a row, a column and a box!
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