September 2017 Update

Task/Sorting-algorithms-Heapsort/SequenceL/sorting-algorithms-heapsort.sequencel

@@ -0,0 +1,32 @@
+import <Utilities/Sequence.sl>;
+
+TUPLE<T> ::= (A: T, B: T);
+
+heapSort(x(1)) :=
+	let
+		heapified := heapify(x, (size(x) - 2) / 2 + 1);
+	in
+		sortLoop(heapified, size(heapified));
+
+heapify(x(1), i) :=
+	x when i <= 0 else
+	heapify(siftDown(x, i, size(x)), i - 1);
+
+sortLoop(x(1), i) :=
+	x when i <= 2 else
+	sortLoop( siftDown(swap(x, 1, i), 1, i - 1), i - 1);
+
+siftDown(x(1), start, end) :=
+	let
+		child := start * 2;
+		child1 := child + 1 when child + 1 <= end and x[child] < x[child + 1] else child;
+	in
+		x when child >= end else
+		x when x[start] >= x[child1] else
+		siftDown(swap(x, child1, start), child1, end);
+
+swap(list(1), i, j) :=
+	let
+		vals := (A: list[i], B: list[j]);
+	in
+		setElementAt(setElementAt(list, i, vals.B), j, vals.A);