Heapsort

• Heapsort is NOT divide and conquer
  • But we have discussed a heap.
  • And I am taking a diversion into sorting.
• Remember the properties of a heap.
• So the general idea is:
  • Given an array, turn it into a max heap.
    • How might we do this?
    • Answer

      
      // assume array index at 0
       For  position = 1 to position size-1 
          HeapifyUp(ary, position)
       EndFor 
       

  • Answer

     
     While heap.size() > 0
         swap(heap[0], heap[size])
         size--
         HeapifyDown(heap, 0, size)
     EndWhile 
     

• Does it work? Why?
• What is the performance?
• Is this in place?
• Is this stable?
• See HeapSort.h