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module Ch2 exposing (getFNR)
import String exposing (join, split)
import Dict
import List exposing (head, tail)
import Maybe exposing (withDefault)
getFNR : String -> Maybe String
getFNR newString =
let chrs = split "" newString
counts x dic = case (Dict.get x dic) of
Nothing -> 0
Just n -> n
doFind dic rfnr cs =
case (head cs) of
Nothing ->
if List.length rfnr == 0 then Nothing
else Just (join "" (List.reverse rfnr))
Just k ->
case (counts k dic) of
0 -> doFind (Dict.insert k 1 dic) (k :: rfnr)
(withDefault [] (tail cs))
m -> doFind (Dict.insert k (m+1) dic)
((findPrevious
(Dict.insert k (m+1) dic) rfnr)
:: rfnr)
(withDefault [] (tail cs))
findPrevious dic nrs =
case (head nrs) of
Nothing -> "#"
Just y ->
case (Dict.get y dic) of
Nothing -> y
Just u -> if u == 1 then y
else findPrevious dic
(withDefault [] (tail nrs))
in
doFind Dict.empty [] chrs
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