Build heap| Full explanation | Example 2 | part 10
The leaf nodes need not to be heapified as they already follow the heap property. Also, the array representation of the complete binary tree contains the level order traversal of the tree.
So the idea is to find the position of the last non-leaf node and perform the heapify operation of each non-leaf node in reverse level order.
Last non-leaf node = parent of last-node.
or, Last non-leaf node = parent of node at (n-1)th index.
or, Last non-leaf node = Node at index ((n-1) - 1)/2.
= (n/2) - 1.