36 lines
958 B
JavaScript
36 lines
958 B
JavaScript
(function () {
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'use strict';
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// permutations :: [a] -> [[a]]
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var permutations = function (xs) {
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return xs.length ? concatMap(function (x) {
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return concatMap(function (ys) {
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return [[x].concat(ys)];
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}, permutations(delete_(x, xs)));
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}, xs) : [[]];
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};
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// GENERIC FUNCTIONS
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// concatMap :: (a -> [b]) -> [a] -> [b]
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var concatMap = function (f, xs) {
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return [].concat.apply([], xs.map(f));
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};
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// delete :: Eq a => a -> [a] -> [a]
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var delete_ = function (x, xs) {
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return deleteBy(function (a, b) {
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return a === b;
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}, x, xs);
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};
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// deleteBy :: (a -> a -> Bool) -> a -> [a] -> [a]
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var deleteBy = function (f, x, xs) {
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return xs.length > 0 ? f(x, xs[0]) ? xs.slice(1) :
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[xs[0]].concat(deleteBy(f, x, xs.slice(1))) : [];
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};
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// TEST
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return permutations(['Aardvarks', 'eat', 'ants']);
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})();
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