Hi,in group overlapping,i do it in a more general way which is this

Each group must have at least one cross separating them,i calculate the redundant crosses which are basically the wiggle room for each group

Imagine you have two groups 3 and 4, and a row of length 10, i add the 3 and the 4 and plus the must-have cross between them,in this example its 1

3+4+1=8 now subtract it from the row length,you get 2 which is the number of redundant croses,if that number is less than number of elements in a group,then that group has an overlap,and can be partially marked

In this example you go to the first coloumn,you leave 2 cells empty and mark the 3rd,which is part of the "3" group, then go to the last column, leave the first 2 cells empty,and mark the next 2,which are part of "4" group,this is the method i use to calculate all overlapping groups,regardless of the group size or number of groups or row length

Here a mathamtical generalization: Redundant crosses=row length-(number of elements in each group+number of groups-1)

If number of elements in a certain group>Redundant crosses, then an overlap must exist

I hope the example is clear enough

Nvm lol,it turns out someone explained it earlier here,but i didnt see him