September Morn Update

Task/Sorting-algorithms-Heapsort/Stata/sorting-algorithms-heapsort.stata

@@ -0,0 +1,44 @@
+function siftup(a, i) {
+	k = i
+	while (k > 1) {
+		p = floor(k/2)
+		if (a[k] > a[p]) {
+			s = a[p]
+			a[p] = a[k]
+			a[k] = s
+			k = p
+		}
+		else break
+	}
+}
+
+function siftdown(a, i) {
+	k = 1
+	while (1) {
+		l = k+k
+		if (l > i) break
+		if (l+1 <= i) {
+			if (a[l+1] > a[l]) l++
+		}
+		if (a[k] < a[l]) {
+			s = a[k]
+			a[k] = a[l]
+			a[l] = s
+			k = l
+		}
+		else break
+	}
+}
+
+function heapsort(a) {
+	n = length(a)
+	for (i = 2; i <= n; i++) {
+		siftup(a, i)
+	}
+	for (i = n; i >= 2; i--) {
+		s = a[i]
+		a[i] = a[1]
+		a[1] = s
+		siftdown(a, i-1)
+	}
+}