September 2017 Update

Task/Pythagorean-triples/JavaScript/pythagorean-triples-1.js

@@ -0,0 +1,43 @@
+(() => {
+
+    // concatMap :: (a -> [b]) -> [a] -> [b]
+    const concatMap = (f, xs) => [].concat.apply([], xs.map(f));
+
+    // range :: Int -> Int -> [Int]
+    const range = (m, n) =>
+        Array.from({
+            length: Math.floor(n - m) + 1
+        }, (_, i) => m + i);
+
+    // gcd :: Integral a => a -> a -> a
+    const gcd = (x, y) => {
+        const _gcd = (a, b) => (b === 0 ? a : _gcd(b, a % b)),
+            abs = Math.abs;
+        return _gcd(abs(x), abs(y));
+    }
+
+    // Arguments: predicate, maximum perimeter
+    // pythTripleCount :: ((Int, Int, Int) -> Bool) -> Int -> Int
+    const pythTripleCount = (p, maxPerim) => {
+        const xs = range(1, Math.floor(maxPerim / 2));
+
+        return  concatMap(x =>
+                concatMap(y =>
+                concatMap(z =>
+                (   (x + y + z     <=  maxPerim ) &&
+                    (x * x + y * y === z * z    ) &&
+                   p(x,  y,  z)                 ) ? [
+                                [x, y, z]
+                    ] :         [       ], // concatMap eliminates empty lists
+                    xs.slice(y)), xs.slice(x)), xs
+                )
+                .length;
+    };
+
+    return [10, 100, 1000]
+        .map(n => ({
+            maxPerimeter: n,
+            triples: pythTripleCount(x => true, n),
+            primitives: pythTripleCount((x, y, _) => gcd(x, y) === 1, n)
+        }));
+})();

Task/Pythagorean-triples/JavaScript/pythagorean-triples-2.js

@@ -0,0 +1,3 @@
+[{"maxPerimeter":10, "triples":0, "primitives":0},
+ {"maxPerimeter":100, "triples":17, "primitives":7},
+ {"maxPerimeter":1000, "triples":325, "primitives":70}]