Data commit

Task/Permutations/JavaScript/permutations-4.js

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