Initial data commit

Task/Sorting-algorithms-Heapsort/E/sorting-algorithms-heapsort.e

@@ -0,0 +1,37 @@
+def heapsort := {
+  def cswap(c, a, b) {
+    def t := c[a]
+    c[a]  := c[b]
+    c[b]  := t
+    # println(c)
+  }
+
+  def siftDown(array, start, finish) {
+    var root := start
+    while (var child := root * 2 + 1
+           child <= finish) {
+      if (child + 1 <= finish && array[child] < array[child + 1]) {
+        child += 1
+      }
+      if (array[root] < array[child]) {
+        cswap(array, root, child)
+        root := child
+      } else {
+        break
+      }
+    }
+  }
+
+  /** Heapsort (in-place). */
+  def heapsort(array) {
+    # in pseudo-code, heapify only called once, so inline it here
+    for start in (0..((array.size()-2)//2)).descending() {
+      siftDown(array, start, array.size()-1)
+    }
+
+    for finish in (0..(array.size()-1)).descending() {
+      cswap(array, 0, finish)
+      siftDown(array, 0, finish - 1)
+    }
+  }
+}