根据给定条件对二叉树中的节点进行计数(递归)

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

def count_nodes(root: TreeNode) -> int:
    if root is None:
        return 0
    else:
        return 1 + count_nodes(root.left) + count_nodes(root.right)

# 创建一个简单的二叉树
#       1
#      / \
#     2   3
#    / \
#   4   5
root = TreeNode(1)
root.left = TreeNode(2)
root.right = TreeNode(3)
root.left.left = TreeNode(4)
root.left.right = TreeNode(5)

# 计算二叉树中的节点数
node_count = count_nodes(root)
print("节点数:", node_count)  # 输出：节点数: 5