Initial data commit

Task/Knuth-shuffle/JavaScript/knuth-shuffle-4.js

@@ -0,0 +1,61 @@
+(() => {
+
+    // knuthShuffle :: [a] -> [a]
+    const knuthShuffle = xs =>
+        enumFromTo(0, xs.length - 1)
+        .reduceRight((a, i) => {
+            const iRand = randomRInt(0, i);
+            return i !== iRand ? (
+                swapped(i, iRand, a)
+            ) : a;
+        }, xs);
+
+    const test = () => knuthShuffle(
+        (`alpha beta gamma delta epsilon zeta
+          eta theta iota kappa lambda mu`)
+        .split(/\s+/)
+    );
+
+    // Non mutating version of swapped
+
+    // swapped :: Int -> Int -> [a] -> [a]
+    const swapped = (iFrom, iTo, xs) =>
+        xs.map(
+            (x, i) => iFrom !== i ? (
+                iTo !== i ? (
+                    x
+                ) : xs[iFrom]
+            ) : xs[iTo]
+        );
+
+    // GENERIC FUNCTIONS ----------------------------------
+
+    // enumFromTo :: Int -> Int -> [Int]
+    const enumFromTo = (m, n) =>
+        n >= m ? (
+            iterateUntil(x => x >= n, x => 1 + x, m)
+        ) : [];
+
+    // iterateUntil :: (a -> Bool) -> (a -> a) -> a -> [a]
+    const iterateUntil = (p, f, x) => {
+        let vs = [x],
+            h = x;
+        while (!p(h))(h = f(h), vs.push(h));
+        return vs;
+    };
+
+    // randomRInt :: Int -> Int -> Int
+    const randomRInt = (low, high) =>
+        low + Math.floor(
+            (Math.random() * ((high - low) + 1))
+        );
+
+    // zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
+    const zipWith = (f, xs, ys) =>
+        Array.from({
+            length: Math.min(xs.length, ys.length)
+        }, (_, i) => f(xs[i], ys[i], i));
+
+    // MAIN ---
+    return test();
+})();