Non-continuous subsequences
You are encouraged to solve this task according to the task description, using any language you may know.
Consider some sequence of elements.
A subsequence contains some, but not all elements of this sequence, in the same order.
A continuous subsequence is missing elements only before its begin and after its end.
The task is to find all non-continous subsequences for a given sequence. Example: For the sequence 1,2,3,4, there are five non-continous subsequences, namely 1,3; 1,4; 2,4; 1,3,4 and 1,2,4.
Haskell
action p x = if p x then succ x else x fenceM p q s [] = guard (q s) >> return [] fenceM p q s (x:xs) = do (f,g) <- p ys <- fenceM p q (g s) xs return $ f x ys ncsubseq = fenceM [((:), action even), (flip const, action odd)] (>= 3) 0
Output:
*Main> ncsubseq [1..3] [[1,3]] *Main> ncsubseq [1..4] [[1,2,4],[1,3,4],[1,3],[1,4],[2,4]] *Main> ncsubseq [1..5] [[1,2,3,5],[1,2,4,5],[1,2,4],[1,2,5],[1,3,4,5],[1,3,4],[1,3,5],[1,3],[1,4,5],[1,4],[1,5],[2,3,5],[2,4,5],[2,4],[2,5],[3,5]]