bst.py

import unittest

def inorderTraversal(root):
    return (inorderTraversal(root.left) + [root.value] + inorderTraversal(root.right)) if root else []

def is_sorted(l):
    return all(a <= b for a, b in zip(l, l[1:]))

def is_binary_search_tree(root):

    # Determine if the tree is a valid binary search tree
    lis = inorderTraversal(root)
    

    return is_sorted(lis)


















# Tests

class Test(unittest.TestCase):

    class BinaryTreeNode(object):

        def __init__(self, value):
            self.value = value
            self.left = None
            self.right = None

        def insert_left(self, value):
            self.left = Test.BinaryTreeNode(value)
            return self.left

        def insert_right(self, value):
            self.right = Test.BinaryTreeNode(value)
            return self.right

    def test_valid_full_tree(self):
        tree = Test.BinaryTreeNode(50)
        left = tree.insert_left(30)
        right = tree.insert_right(70)
        left.insert_left(10)
        left.insert_right(40)
        right.insert_left(60)
        right.insert_right(80)
        result = is_binary_search_tree(tree)
        self.assertTrue(result)

    def test_both_subtrees_valid(self):
        tree = Test.BinaryTreeNode(50)
        left = tree.insert_left(30)
        right = tree.insert_right(80)
        left.insert_left(20)
        left.insert_right(60)
        right.insert_left(70)
        right.insert_right(90)
        result = is_binary_search_tree(tree)
        self.assertFalse(result)

    def test_descending_linked_list(self):
        tree = Test.BinaryTreeNode(50)
        left = tree.insert_left(40)
        left_left = left.insert_left(30)
        left_left_left = left_left.insert_left(20)
        left_left_left.insert_left(10)
        result = is_binary_search_tree(tree)
        self.assertTrue(result)

    def test_out_of_order_linked_list(self):
        tree = Test.BinaryTreeNode(50)
        right = tree.insert_right(70)
        right_right = right.insert_right(60)
        right_right.insert_right(80)
        result = is_binary_search_tree(tree)
        self.assertFalse(result)

    def test_one_node_tree(self):
        tree = Test.BinaryTreeNode(50)
        result = is_binary_search_tree(tree)
        self.assertTrue(result)


unittest.main(verbosity=2)