to get the total number of pairwise combinations.

items -> []Item, return []string -> []Id.

here is the entry for pairwise algorithm 1.

to get the item matrix with type Item.

to define the item for each element.

Note: in Python, key_cache (KeyCache) is dict, with tuple(items) as key, tuple(ids) is value { (<allpairspy.allpairs.Item object at 0x1015dd2e8>,): ('a0v0',), (<allpairspy.allpairs.Item object at 0x1015dd358>,): ('a0v1',), (<allpairspy.allpairs.Item object at 0x1015dd3c8>,): ('a0v2',) }.

for the element already added / arranged.

for the elements already added / arranged.

Below is for pairwise data.

Implements the Interface in sort package, used for Item sort type Interface interface { Len() int Less(i, j int) bool Swap(i, j int) }.