leetcode_gym/_problems/countCompleteBinaryNodes.md

layout, title, last_solved, category, leetcode_url, status

layout	title	last_solved	category	leetcode_url	status
page	Count Complete Tree Nodes	2020-06-23	trees	https://leetcode.com/problems/count-complete-tree-nodes/	Attempted

Problem

Given a complete binary tree, count the number of nodes.

Note:

Definition of a complete binary tree from Wikipedia:
In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.

Example:

Input: 
    1
   / \
  2   3
 / \  /
4  5 6

Output: 6

Solution

There should be a better way to do this than O(n) if you take advantage of the complete binary tree property.

{% highlight python %}

def countNodes(self, root: TreeNode) -> int:

if not root:
    return 0

leftRes = self.countNodes(root.left)
rightRes = self.countNodes(root.right)

return 1 + leftRes + rightRes

{% endhighlight %}