以下代码能够正确统计二叉树中叶子结点的数量。（ ）
class TreeNode:
def __init__(self, val=0, left=None, right=None):
self.val = val
self.left = left
self.right = right
def count_leaf(root):
if not root:
return 0
if not root.left and not root.right:
return 1
return count_leaf(root.left) + count_leaf(root.right)
if __name__ == "__main__":
root1 = TreeNode(1)
root1.left = TreeNode(2)
root1.right = TreeNode(3)
root1.left.left = TreeNode(4)
root1.left.right = TreeNode(5)
root1.right.right = TreeNode(6)
print(f"二叉树1的叶子节点数：{count_leaf(root1)}")
root2 = TreeNode(1)
print(f"二叉树2的叶子节点数：{count_leaf(root2)}") 1
root3 = None
print(f"空树的叶子节点数：{count_leaf(root3)}")