Department numbers: Difference between revisions

'use strict';

// NUMBERING CONSTRAINTS --------------------------------------------------

const options = (lo, hi, total) => {

bind = flip(concatMap),

ds = enumFromTo(lo, hi);

return bind(filter(even, ds),

x => bind(filter(d => d !== x, ds),

y => bind([total - (x + y)],

)

// GENERIC FUNCTIONS ------------------------------------------------------

// concatMap :: (a -> [b]) -> [a] -> [b]

const concatMap = (f, xs) => [].concat.apply([], xs.map(f));

const enumFromTo = (m, n) =>

Array.from({

length: Math.floor(n - m) + 1

// filter :: (a -> Bool) -> [a] -> [a]

const filter = (f, xs) => xs.filter(f);

// flip :: (a -> b -> c) -> b -> a -> c

const flip = f => (a, b) => f.apply(null, [b, a]);

// length :: [a] -> Int

const length = xs => xs.length;

// map :: (a -> b) -> [a] -> [b]

const map = (f, xs) => xs.map(f);

// show :: a -> String

const show = x => JSON.stringify(x) //, null, 2);

// unlines :: [String] -> String

const unlines = xs => xs.join('\n');

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

const xs = options(1, 7, 12);

return '(Police, Sanitation, Fire)\n\n' +

unlines(map(show, xs)) +

'\n\nNumber of options: ' + length(xs);