House Robber III

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def rob(self, root: Optional[TreeNode]) -> int:
        #function returns a tuple (e1, e2) where e1 is amt robbed including the subtree's root while e2 is amt without subtree's root
        def help(root):
            if not root:
                return (0, 0)
            #postorder
            a,b = help(root.left)
            c, d = help(root.right)
            return(b+d+root.val,max(a, b)+max(c,d))
        return max(help(root))