LeetCode. Count Complete Tree Nodes

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:

-Summary-

Solve by recursion

1. if the root exists, we add 1 then move to the left and right subtree.

2. if the root is None, return 0.

 

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def countNodes(self, root: TreeNode) -> int:
        return 1+self.countNodes(root.left)+self.countNodes(root.right) if root else 0

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