Unique characters: Difference between revisions

=={{header|JavaScript}}==

<lang javascript>(() => {

"use strict";

// ---------------- UNIQUE CHARACTERS ----------------

// uniques :: String -> [Char]

const uniques = xs =>

group(

xs.flatMap(x => [...x])

.sort()

)

.flatMap(

x => 1 === x.length ? (

x

) : []

);

// ---------------------- TEST -----------------------

// main :: IO ()

const main = () =>

uniques([

"133252abcdeeffd",

"a6789798st",

"yxcdfgxcyz"

]);

// --------------------- GENERIC ---------------------

// group :: Eq a => [a] -> [[a]]

const group = xs => {

// A list of lists, each containing only equal elements,

// such that the concatenation of these lists is xs.

const go = ys =>

0 < ys.length ? (() => {

const

h = ys[0],

i = ys.findIndex(y => h !== y);

return i !== -1 ? (

[ys.slice(0, i)].concat(go(ys.slice(i)))

) : [ys];

})() : [];

return go(xs);

};

// MAIN ---

return JSON.stringify(main());

})();</lang>

{{Out}}

<pre>["1","5","6","b","g","s","t","z"]</pre>