Problem URL: Equal tree partition

Cutting an edge means cutting off a proper subtree (i.e., a subtree but not the whole tree). I collect the sums of these proper subtrees in a set and check whether half the total tree sum is a possible cut.

# 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 checkEqualTree(self, root: Optional[TreeNode]) -> bool:
        def sum(node):
            if not node:
                return 0
            s = node.val + sum(node.left) + sum(node.right)
            if node is not root:
                cuts.add(s)
            return s

        cuts = set()
        return sum(root) / 2 in cuts

Time complexity: O(n), where n is the number of nodes in the tree
Space complexity: O(n)