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

Note:

Definition of a complete binary tree from :

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 6Output: 6

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有很多种方法，直接用bfs算法统计每层个数即可。

class Solution:    def countNodes(self, root: TreeNode) -> int:        if root is None:return 0        bfs=[root]        sums=0        while bfs:            sums+=len(bfs)            temp=[]            for node in bfs:                if node.left:                    temp.append(node.left)                if node.right:                    temp.append(node.right)            bfs=temp        return sums

 

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