Add dominoes

[keiravillekode]

No description provided.

[fapdash]

Really cool example solution, although my graph theory is not strong enough to fully follow. 😅

Great addition! :)

[keiravillekode]

I added some comments when publishing my community solution.

; For the dominoes to chain, it is necessary and sufficient that
; - each number appears an even number of times
; - each number present is reachable from any other number present

; We use a `tally` vector to record how many times each number appears.

; We use a Disjoint Set `parent` vector to merge sets of reachable numbers.