LeetCode 222. Count Complete Tree Nodes

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题目

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 2^h nodes inclusive at the last level h.

Example:

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

Output: 6

思路

Recursive.

代码

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# # Definition for a binary tree node.
# # class TreeNode(object):
# #     def __init__(self, val=0, left=None, right=None):
# #         self.val = val
# #         self.left = left
# #         self.right = right
# class Solution(object):
#     def countNodes(self, root):
#         """
#         :type root: TreeNode
#         :rtype: int
#         """
#         if not root:
#             return 0
#         nodes = 0
#         left = self.getHeight(root.left)
#         right = self.getHeight(root.right)
#         if left == right:
#             nodes = 2 ** left + self.countNodes(root.right)
#         else:
#             nodes = 2 ** right +self.countNodes(root.left)
#         return nodes
    
    
#     def getHeight(self, root):
#         height = 0
#         while root:
#             height += 1
#             root = root.left
#         return height


# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
    def countNodes(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if not root:
            return 0
        return 1 + self.countNodes(root.left) + self.countNodes(root.right)