222.md

222. Count Complete Tree Nodes

Solution 1 (time O(n), space O(1))

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def countNodes(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if root is None:
            return 0
        left = self.countLevel(root.left)
        right = self.countLevel(root.right)
        if left == right:
            return self.countNodes(root.right) + (1 << left)
        else:
            return self.countNodes(root.left) + (1 << right)

    def countLevel(self, root):
        level = 0
        while root is not None:
            level += 1
            root = root.left
        return level

Solution 2 (time O(log(n)^2), space O(1))

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def countNodes(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if root is None:
            return 0
        return 1 + self.countNodes(root.left) + self.countNodes(root.right)