// https://leetcode.com/problems/validate-binary-search-tree/

class TreeNode(_value: Int = 0, _left: TreeNode = null, _right: TreeNode = null) {
  var value: Int = _value
  var left: TreeNode = _left
  var right: TreeNode = _right
}

object Solution {
  def isValidBST(root: TreeNode): Boolean = {

    implicit class isBetween(curr: TreeNode) {
      def isBetween(from: Long, to: Long) = curr.value > from && curr.value < to
    }

    def go(root: TreeNode, from: Long, to: Long): Boolean = {
      if(root == null) true
      else {
        root.isBetween(from, to) &&
        go(root.left, from, root.value) &&
        go(root.right, root.value, to)
      }
    }

    go(root, Long.MinValue, Long.MaxValue)
  }
}