Validate Binary Search Tree Problem Statement

Given a binary tree with 'N' nodes, determine if it is a Binary Search Tree (BST). Return true if the tree is a BST, otherwise return false.

Example:

Input:

1 2 3 4 -1 5 6 -1 7 -1 -1 -1 -1 -1 -1

Output:

true

Explanation:

The tree is a valid Binary Search Tree because it satisfies the following properties:

• The left subtree of a node contains only nodes with values less than the node’s value.
• The right subtree of a node contains only nodes with values greater than the node’s value.
• Both the left and right subtrees must also be binary search trees.

Input:

The first line contains an integer 't', the number of test cases. For each test case, the elements of the tree are provided in level order, with '-1' indicating a null node.

Output:

For each test case, output 'true' if the tree is a BST, otherwise output 'false'. Each result is printed on a new line.

Constraints:

• 1 <= T <= 100
• 1 <= N <= 1000
• -10^6 <= data <= 10^6
• Duplicate elements can be in either the left or right subtree.

Note:

You do not need to print anything explicitly. Implement the function to return the required results.