如何判断到达叶子(if not root.left and not root.right:)
class Solution(object):
def sumNumbers(self, root):
"""
:type root: TreeNode
:rtype: int
"""
if not root:
return 0
res=[0]
def dfs(root,s):
if not root.left and not root.right:
res[0]+=int(s+str(root.val))
return
if root.left:
dfs(root.left,s+str(root.val))
if root.right:
dfs(root.right,s+str(root.val))
dfs(root,'')
return res[0]