Find the missing permutation: Difference between revisions

})();</lang>

{{Out}}

<pre>DBAC</pre>

====XOR====

Folding an xor operator over the list of character codes:

<lang javaScript>(() => {

'use strict';

// main :: IO ()

const main = () => {

const xs = [

'ABCD', 'CABD', 'ACDB', 'DACB', 'BCDA', 'ACBD',

'ADCB', 'CDAB', 'DABC', 'BCAD', 'CADB', 'CDBA',

'CBAD', 'ABDC', 'ADBC', 'BDCA', 'DCBA', 'BACD',

'BADC', 'BDAC', 'CBDA', 'DBCA', 'DCAB'

];

return xs.slice(1).reduce(

(a, x) => zipWith(xor)(a)(codes(x)),

codes(xs[0])

).map(x => String.fromCodePoint(x)).join('')

};

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

// codes :: String -> [Int]

const codes = s =>

s.split('').map(c => c.codePointAt(0));

// xor :: Int -> Int -> Int

const xor = a =>

b => (a ^ b)

// zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]

const zipWith = f =>

// A list constructed by zipping with a

// custom function, rather than with the

// default tuple constructor.

xs => ys => xs.slice(0).map(

(x, i) => f(x)(ys[i])

);

return main()