2016 Update

Task/Spiral-matrix/JavaScript/spiral-matrix-4.js

@@ -0,0 +1,67 @@
+(n => {
+
+    // spiral :: the first row plus a smaller spiral rotated 90 degrees clockwise
+    // spiral :: Int -> Int -> Int -> [[Int]]
+    function spiral(lngRows, lngCols, nStart) {
+        return lngRows ? [range(nStart, (nStart + lngCols) - 1)]
+            .concat(
+                transpose(
+                    spiral(lngCols, lngRows - 1, nStart + lngCols)
+                )
+                .map(reverse)
+            ) : [[]];
+    }
+
+    // transpose :: [[a]] -> [[a]]
+    function transpose(xs) {
+        return xs[0]
+            .map((_, iCol) => xs
+                .map((row) => row[iCol]));
+    }
+
+    // reverse :: [a] -> [a]
+    function reverse(xs) {
+        return xs.slice(0)
+            .reverse();
+    }
+
+    // range(intFrom, intTo, optional intStep)
+    // Int -> Int -> Maybe Int -> [Int]
+    function range(m, n, step) {
+        let d = (step || 1) * (n >= m ? 1 : -1);
+
+        return Array.from({
+            length: Math.floor((n - m) / d) + 1
+        }, (_, i) => m + (i * d));
+    }
+
+
+
+    // TESTING
+
+    // replicate :: Int -> String -> String
+    function replicate(n, a) {
+        var v = [a],
+            o = '';
+
+        if (n < 1) return o;
+        while (n > 1) {
+            if (n & 1) o = o + v;
+            n >>= 1;
+            v = v + v;
+        }
+        return o + v;
+    }
+
+
+    return spiral(n, n, 0)
+        .map(
+            xs => xs.map(x => {
+                let s = `${x}`;
+                return replicate(4 - s.length, ' ') + s;
+            })
+            .join('')
+        )
+        .join('\n');
+
+})(5);