How is the memory of the array of segment tree 2 * 2 ^(ceil(log(n))) - 1?

Question

The link: http://www.geeksforgeeks.org/segment-tree-set-1-sum-of-given-range/. This is the quoted text:

We start with a segment arr[0 . . . n-1]. And ever

Answer 1

Let the size of input array is n.
All the input array elements will be leaf nodes in segment tree so the number of leaf nodes = n
Since the Segment tree is a complete tree so the Hight of Segment Tree h = ⌈ Log₂n ⌉ + 1
Maximum number of nodes in a binary tree of height ‘h’ is 2^h-1

So Number of nodes in a segment tree = 2^{⌈ Log₂n ⌉ + 1} -1
Equals to 2*2^{⌈ Log₂n ⌉} -1