Count Complete Tree Nodes
Given the root of a complete binary tree, return the number of the nodes in the tree.
According to Wikipedia, every level, except possibly the last, is completely filled in a complete binary tree, and all nodes in the last level are as far left as possible. It can have between 1 and 2^h nodes inclusive at the last level h.
Design an algorithm that runs in less than O(n) time complexity.
Example 1
1
/ \
2 3
/ \ /
4 5 6Input
root = [1,2,3,4,5,6]Output
6The complete binary tree contains 6 nodes.
Example 2
[]
Input
root = []Output
0The tree is empty, so it contains 0 nodes.
Constraints
- The number of nodes in the tree is in the range
[0, 5 * 10^4]. 0 <= Node.val <= 5 * 10^4- The tree is guaranteed to be complete.