two.rb

require_relative 'jubilib/binary_tree'

def is_valid_bst(node, min = -Float::INFINITY, max = Float::INFINITY)
  return true if node.nil?
  return false unless node.val > min and node.val < max
  return (is_valid_bst(node.left, min, [max, node.val].min) and
    is_valid_bst(node.right, [min, node.val].max, max))
end