2016 Update

Task/Levenshtein-distance/JavaScript/levenshtein-distance-2.js

@@ -0,0 +1,73 @@
+(() => {
+    'use strict';
+
+    // levenshtein :: String -> String -> Int
+    const levenshtein = (sa, sb) => {
+        const [s1, s2] = [sa.split(''), sb.split('')];
+
+        return last(s2.reduce((ns, c) => {
+            const [n, ns1] = uncons(ns);
+
+            return scanl(
+                (z, [c1, x, y]) =>
+                minimum(
+                    [y + 1, z + 1, x + fromEnum(c1 != c)]
+                ),
+                n + 1,
+                zip3(s1, ns, ns1)
+            );
+        }, range(0, s1.length)));
+    };
+
+
+    /*********************************************************************/
+    // GENERIC FUNCTIONS
+
+    // minimum :: [a] -> a
+    const minimum = xs =>
+        xs.reduce((a, x) => (x < a || a === undefined ? x : a), undefined);
+
+    // fromEnum :: Enum a => a -> Int
+    const fromEnum = x => {
+        const type = typeof x;
+        return type === 'boolean' ? (
+            x ? 1 : 0
+        ) : (type === 'string' ? x.charCodeAt(0) : undefined);
+    };
+
+    // uncons :: [a] -> Maybe (a, [a])
+    const uncons = xs => xs.length ? [xs[0], xs.slice(1)] : undefined;
+
+    // scanl :: (b -> a -> b) -> b -> [a] -> [b]
+    const scanl = (f, a, xs) => {
+        for (var lst = [a], lng = xs.length, i = 0; i < lng; i++) {
+            a = f(a, xs[i], i, xs), lst.push(a);
+        }
+        return lst;
+    };
+
+    // zip3 :: [a] -> [b] -> [c] -> [(a,b,c)]
+    const zip3 = (xs, ys, zs) =>
+        xs.slice(0, Math.min(xs.length, ys.length, zs.length))
+        .map((x, i) => [x, ys[i], zs[i]]);
+
+    // last :: [a] -> a
+    const last = xs => xs.length ? xs.slice(-1) : undefined;
+
+    // range :: Int -> Int -> [Int]
+    const range = (m, n) =>
+        Array.from({
+            length: Math.floor(n - m) + 1
+        }, (_, i) => m + i);
+
+    /*********************************************************************/
+    // TEST
+    return [
+        ["kitten", "sitting"],
+        ["sitting", "kitten"],
+        ["rosettacode", "raisethysword"],
+        ["raisethysword", "rosettacode"]
+    ].map(pair => levenshtein.apply(null, pair));
+
+    // -> [3, 3, 8, 8]
+})();