Duncan's SuDoku Solver

This is a version 14.0 screenshot

Must-have Combinations:

This analysis assesses if a Group must have a particular value present somewhere within in it, based on its size and the remaining possibles.

In this example, the Group made up of Squares A4, A5 and B4 must sum to 8. The are only two possibilities: 1/2/5 or 1/3/4. Either way, there must be a 1 somewhere in the Group (highlighted in blue).

If all the possible 1's in the Group are contained within the same Row, Column or Box then some possibles can be eliminated (outlined in orange).

This is a version 14.0 screenshot

Must-have Combinations:

In this second example, the four-square Group made up of B8, B9, C8 and C9 must sum to 12. The only possibilities are 1/2/3/6 or 1/2/4/5. Either way, there must be a 1 and a 2 somewhere in the Group (highlighted in blue).

All the 1s and 2s in the Group are contained in the top-right Box. Any other 1s and 2s in this Box can be eliminated (outlined in orange).

This is a version 14.0 screenshot

Must-have Combinations:

In this third example, the four-square Group made up of D1, E1, F1 and G1 must sum to 12. The only possibilities are 1/2/3/6 or 1/2/4/5. Either way, there must be a 1 and a 2 somewhere in the Group (highlighted in blue).

All the 1s and 2s in the Group are contained in the left Column. Any other 1s and 2s in this Column can be eliminated (outlined in orange). Moreover, all the 1s in the Group are contained in the middle-left Box, so the other 1s in this Box can be eliminated.

© Duncan Nightingale 2026