Solving Classic Sudoku: 'Single Position'

This is the easiest technique of finding out a number. Select a row/column/box (preferably with many given numbers) and find out the numbers remaining. Using other given numbers, try to find a unique position of one of the remaining numbers of the chosen row/column/box.

Take a look at Puzzle No.144. We select the 5th column as it has 4 given numbers. Since there is a '1' in the box above the centre box and the box below the centre box (which should be identified visually), let us try to find the position of '1' in the 5th column.


All possible positions of '1' in the 5th column are marked in green.


'1' cannot be placed in the top two and bottom two cells of the 5th column because '1' will then be repeated in a box as there is already a '1' in the two boxes.


There is only one unique position remaining for the '1' in the 5th column.

Other Solving Techniques