176. Count Complete Tree Nodes
EasyTree
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.
Examples
Input: [1,2,3,4,5,6]
Output: 6
Explanation: The complete tree has 6 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.
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