A path should contain at least two nodes, therefore the example below is wrong:

Your Input: [1, -2, -3] Output: -1 Expected: 1

1. Keep in mind that you need to check path every node. Not every leaf as it was in before problem.
2. Consider if you need to sum a negative path.

lass Solution:
  
  def dfs(self, node):
    if not node:
      return 0

    left = self.dfs(node.left)
    right = self.dfs(node.right)

    path = 0 
    if right > 0 and left < 0:
      path = right + node.val
    elif left > 0 and right < 0:
      path = left + node.val
    else: 
      path = left + right + node.val

    self.max_path = max(self.max_path, path)

    return max(left, right) + node.val

  def findMaximumPathSum(self, root):
    self.max_path = root.val
    self.dfs(root)
    return self.max_path