对二叉树中的节点进行计数

class TreeNode:
    def __init__(self, value=0, left=None, right=None):
        self.value = value
        self.left = left
        self.right = right

def count_nodes(root):
    if root is None:
        return 0
    return 1 + count_nodes(root.left) + count_nodes(root.right)

from collections import deque

def count_nodes_iterative(root):
    if root is None:
        return 0
    queue = deque([root])
    count = 0
    while queue:
        node = queue.popleft()
        count += 1
        if node.left:
            queue.append(node.left)
        if node.right:
            queue.append(node.right)
    return count