grouping values in less as possible domains

hello together,

I am dealing around with a problem I cannot solve.

Imagine you have a list of curves and you measure the lenght of each one.

Now you give a  positive and negative "tolerance"(here of 1) to each length. For example you have a length of ten and you create a domain from 9 to 11. later you want to group all lines by as less as possible domains.

If you have a look to the image...you see 6 lines and their red dotted ranges. to group them by the domain of 3 and 5 would be the best result with the less domains. (here 2)

if you would use the domain of line 0,1 or 3 you could not include line 4 and you would have 3 instead of just 2 groups.....

later on it is important for me to group as much as possible lines in less as possible domains.

I hope this is somehow understandable.