Duncan's SuDoku Solver

This is a version 14.0 screenshot

One Square:

Taking advantage of 'The 45 Rule' (every Row, Column and Box consists of the numbers 1 to 9 and so must sum to 45), this analysis looks for a set of Rows, Columns or Boxes that is missing one Square (or has one extra Square). The value of this one Square is then easily determined.

In this example, the Killer Groups outlined in red form a set consisting of the middle-left Box plus G1. The set of Killer Groups sums to 46. Since the middle-left Box must sum to 45 (the 45 rule), then G1 must have the value 1.

This is a version 14.0 screenshot

One Square:

In this second example, the Killer Groups outlined in red form a set consisting of the top four Rows plus E5. The set of Killer Groups sums to 186. Since the top four Rows must sum to 180 (4 X the 45 rule), E5 must have the value 6.

This is a version 14.0 screenshot

One Square:

In this third example, the Killer Groups outlined in red form a set consisting of the top two Rows, minus B8. The set of Killer Groups sums to 84. Since the top two Rows sum to 90 (2 X the 45 rule), B8 must have the value 6.

© Duncan Nightingale 2026