equal-tree-partition.py

# Time:  O(n)
# Space: O(n)

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def checkEqualTree(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        def getSumHelper(node, lookup):
            if not node:
                return 0
            total = node.val + \
                    getSumHelper(node.left, lookup) + \
                    getSumHelper(node.right, lookup)
            lookup[total] += 1
            return total

        lookup = collections.defaultdict(int)
        total = getSumHelper(root, lookup)
        if total == 0:
            return lookup[total] > 1
        return total%2 == 0 and (total/2) in lookup