Check for BST.py

class Solution:
    def isBST(self, root, min=float("-inf"), max=float("inf")):
        if root is None:
            return True
        if root.data <= min or root.data >= max:
            return False
        return self.isBST(root.left, min=min, max=root.data) and self.isBST(
            root.right, min=root.data, max=max
        )


# {
# Driver Code Starts
# Initial Template for Python 3
from collections import deque


# Tree Node
class Node:
    def __init__(self, val):
        self.right = None
        self.data = val
        self.left = None


# Function to Build Tree
def buildTree(s):
    # Corner Case
    if len(s) == 0 or s[0] == "N":
        return None

    # Creating list of strings from input
    # string after spliting by space
    ip = list(map(str, s.split()))

    # Create the root of the tree
    root = Node(int(ip[0]))
    size = 0
    q = deque()

    # Push the root to the queue
    q.append(root)
    size = size + 1

    # Starting from the second element
    i = 1
    while size > 0 and i < len(ip):
        # Get and remove the front of the queue
        currNode = q[0]
        q.popleft()
        size = size - 1

        # Get the current node's value from the string
        currVal = ip[i]

        # If the left child is not null
        if currVal != "N":
            # Create the left child for the current node
            currNode.left = Node(int(currVal))

            # Push it to the queue
            q.append(currNode.left)
            size = size + 1
        # For the right child
        i = i + 1
        if i >= len(ip):
            break
        currVal = ip[i]

        # If the right child is not null
        if currVal != "N":
            # Create the right child for the current node
            currNode.right = Node(int(currVal))

            # Push it to the queue
            q.append(currNode.right)
            size = size + 1
        i = i + 1
    return root


if __name__ == "__main__":
    s = "10 5 18 2 9 15 19 N 4 8 N 1"
    root = buildTree(s)
    if Solution().isBST(root):
        print(1)
    else:
        print(0)
# } Driver Code Ends