Unique characters: Difference between revisions
Add two StandardML versions
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156bgstz
</pre>
=={{header|Standard ML}}==
Using an Array:
<syntaxhighlight lang="sml">
fun uniqueChars xs =
let
val arr = Array.array(256, 0)
val inc = (fn c => Array.update(arr, ord c, Array.sub(arr, ord c)+1))
val _ = List.app inc (List.concat (List.map String.explode xs))
val ex1 = (fn (i,n,a) => if n=1 then (chr i)::a else a)
in
String.implode (Array.foldri ex1 [] arr)
end
</syntaxhighlight>
{{out}}
<pre>
- uniqueChars ["133252abcdeeffd","a6789798st","yxcdfgxcyz"];
val it = "156bgstz" : string
</pre>
A different approach:
<syntaxhighlight lang="sml">
(*
group [1,1,2,4,4,4,2,2,2,1,1,1,3]
=> [[1,1], [2], [4,4,4], [2,2,2], [1,1,1], [3]]
*)
fun group xs =
let
fun collectGroups(a,[]) = [[a]]
| collectGroups(a,b::bs) = if a = (hd b) then (a::b)::bs else [a]::b::bs
in
List.foldr collectGroups [] xs
end
fun uniqueChars2 xs =
let
(* turn the strings into one big list of characters *)
val cs = List.concat (List.map String.explode xs)
(* sort the big list of characters *)
val scs = ListMergeSort.sort Char.> cs
(* collect the groups *)
val gs = group scs
(* filter out groups with more than one member *)
val os = List.filter (fn a => null (tl a)) gs
in
String.implode (List.concat os)
end
</syntaxhighlight>
=={{header|V (Vlang)}}==
| |||