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Task/Sorting-algorithms-Heapsort/PureBasic/sorting-algorithms-heapsort.purebasic

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+Declare heapify(Array a(1), count)
+Declare siftDown(Array a(1), start, ending)
+
+Procedure heapSort(Array a(1), count)
+  Protected ending=count-1
+  heapify(a(), count)
+  While ending>0
+    Swap a(ending),a(0)
+    siftDown(a(), 0, ending-1)
+    ending-1
+  Wend
+EndProcedure
+
+Procedure heapify(Array a(1), count)
+  Protected start=(count-2)/2
+  While start>=0
+    siftDown(a(),start,count-1)
+    start-1
+  Wend
+EndProcedure
+
+Procedure siftDown(Array a(1), start, ending)
+  Protected root=start, child
+  While (root*2+1)<=ending
+    child=root*2+1
+    If child+1<=ending And a(child)<a(child+1)
+      child+1
+    EndIf
+    If a(root)<a(child)
+      Swap a(root), a(child)
+      root=child
+    Else
+      Break
+    EndIf
+  Wend
+EndProcedure