题解 | #牛群仰视图#先序遍历所有节点，找到叶子结点

# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param root TreeNode类 
# @return int整型一维数组
#
class Solution:
    def bottomView(self , root: TreeNode) -> List[int]:
        # write code here
        res=[]
        def preOrder(root,res):
            if(root==None):
                return res
            if(root.left==None and root.right==None):
                res.append(root.val)
            preOrder(root.left,res)
            preOrder(root.right,res)
            return res

        ans=preOrder(root,res)
        return ans