2016 Update

Task/Zig-zag-matrix/JavaScript/zig-zag-matrix-4.js

@@ -0,0 +1,60 @@
+(n => {
+
+    // diagonals :: n -> [[n]]
+    function diagonals(n) {
+        let diags = (xs, iCol, iRow) => {
+            if (iCol < xs.length) {
+                let xxs = splitAt(iCol, xs);
+
+                return [xxs[0]].concat(diags(
+                    xxs[1],
+                    iCol + (iRow < n ? 1 : -1),
+                    iRow + 1
+                ));
+            } else return [xs];
+        }
+
+        return diags(range(0, n * n - 1), 1, 1);
+    }
+
+
+    // Recursively read off n heads of diagonal lists
+    // rowsFromDiagonals :: n -> [[n]] -> [[n]]
+    function rowsFromDiagonals(n, lst) {
+        if (lst.length) {
+            let [edge, rest] = splitAt(n, lst);
+
+            return [edge.map(x => x[0])]
+                .concat(rowsFromDiagonals(n,
+                    edge.filter(x => x.length > 1)
+                    .map(x => x.slice(1))
+                    .concat(rest)
+                ));
+        } else return [];
+    }
+
+    // GENERIC FUNCTIONS
+
+    // splitAt :: Int -> [a] -> ([a],[a])
+    function splitAt(n, xs) {
+        return [xs.slice(0, n), xs.slice(n)];
+    }
+
+    // range :: From -> To -> Maybe Step -> [Int]
+    // range :: 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));
+    }
+
+    // ZIG-ZAG MATRIX
+
+    return rowsFromDiagonals(n,
+        diagonals(n)
+        .map((x, i) => (i % 2 || x.reverse()) && x)
+    );
+
+})(5);