## Credit: https://www.geeksforgeeks.org/a-program-to-check-if-a-binary-tree-is-bst-or-not/
## Python program to check if a binary tree is bst or not
 
INT_MAX = 4294967296
INT_MIN = -4294967296
 
# A binary tree node
class Node:

    # Constructor to create a new node
    def __init__(self, data):
        self.data = data
        self.left = None
        self.right = None


# Returns true if the given tree is a binary search tree (efficient version)
def isBST(node):
    return isBSTUtil(node, INT_MIN, INT_MAX)
 
# Retusn true if the given tree is a BST and its values
# >= min and <= max
def isBSTUtil(node, mini, maxi):

    # An empty tree is BST
    if node is None:
        return True

    # False if this node violates min/max constraint
    if node.data < mini or node.data > maxi:
        return False
 
    # Otherwise check the subtrees recursively
    # tightening the min or max constraint
    return (isBSTUtil(node.left, mini, node.data - 1) and isBSTUtil(node.right, node.data + 1, maxi))

# Driver program to test above function

### Example 1
# root = Node(8)
# root.left = Node(5)
# root.right = Node(9)
# root.left.left = Node(4)
# root.left.right = Node(6)


root = Node(5)
root.left = Node(4)
root.right = Node(7)
root.left.left = Node(3)
root.left.right = Node(6)


if (isBST(root)):
    print "1 as the given tree is a BST."
else:
    print "0 as the given tree is a not BST."

# This code is contributed by Nikhil Kumar Singh (nickzuck_007)