2016 Update

Task/Hofstadter-Q-sequence/JavaScript/hofstadter-q-sequence-2.js

@@ -0,0 +1,40 @@
+(() => {
+    'use strict';
+
+    // hofQSeq :: Int -> [Int]
+    const hofQSeq = x =>
+        x > 2 ? tail(foldl((Q, n) =>
+            n < 3 ? Q : Q.concat(
+                Q[n - Q[n - 1]] + Q[n - Q[n - 2]]
+            ), [0, 1, 1],
+            range(1, x))) : (x > 0 ? take(x, [1, 1]) : undefined);
+
+
+    // GENERIC FUNCTIONS -------------------------------------------
+
+    // foldl :: (b -> a -> b) -> b -> [a] -> b
+    const foldl = (f, a, xs) => xs.reduce(f, a),
+
+        // range :: Int -> Int -> [Int]
+        range = (m, n) =>
+            Array.from({
+                length: Math.floor(n - m) + 1
+            }, (_, i) => m + i),
+
+        // tail :: [a] -> [a]
+        tail = xs => xs.length ? xs.slice(1) : undefined,
+
+        // last :: [a] -> a
+        last = xs => xs.length ? xs.slice(-1)[0] : undefined,
+
+        // Int -> [a] -> [a]
+        take = (n, xs) => xs.slice(0, n);
+
+    // TEST --------------------------------------------------------
+    return {
+        firstTen: hofQSeq(10),
+        thousandth: last(hofQSeq(1000)),
+        'Q<Q-1UpTo10E5': hofQSeq(100000)
+            .reduce((a, x, i, xs) => x < xs[i - 1] ? a + 1 : a, 0)
+    };
+})();

Task/Hofstadter-Q-sequence/JavaScript/hofstadter-q-sequence-3.js

@@ -0,0 +1,3 @@
+{"firstTen":[1, 1, 2, 3, 3, 4, 5, 5, 6, 6],
+ "thousandth":502,
+ "Q<Q-1UpTo10E5":49798}