-/**
- * https://leetcode.com/problems/maximum-sum-bst-in-binary-tree/
- * 
- * 
- */ 
 /**
  * https://leetcode.com/problems/maximum-sum-bst-in-binary-tree/
  * 

        let leftSum: Int
        let rightSum: Int
        
        if let left = root.left {
            let (lvalid, lmin, lmax, lsum) = self.validBST(left)
            if lmax >= minV { isValid = false }

 *     }
 * }
 */

 /**
  *
  *  
  */
class Solution {
    func maxSumBST(_ root: TreeNode?) -> Int {
        // Init.
        self.maxSum = 0
        
        guard let root = root else { return self.maxSum }
