# Binary Search Tree Validation - Amazon Top Interview Questions

### Problem Statement :

```Given a binary tree root, return whether it's a binary search tree. A binary tree node is a binary search tree if :

All nodes on its left subtree are smaller than node.val
All nodes on its right subtree are bigger than node.val
All nodes hold the these properties.
Constraint

n ≤ 100,000 where n is the number of nodes in root

Example 1

Input

root = [3, [2, null, null], [9, [7, [4, null, null], [8, null, null]], [12, null, null]]]

Output

True

Example 2

Input

root = [3, [1, null, null], [5, [4, null, [7, null, null]], [6, null, null]]]

Output

False

Explanation

This is not a binary search tree because the 7 is not smaller than 5.```

### Solution :

```                        ```Solution in C++ :

bool isBST(Tree* root, int lo, int hi) {
if (root == NULL) return 1;
if (root->val < lo or root->val > hi) return 0;

return isBST(root->left, lo, root->val) and isBST(root->right, root->val, hi);
}

bool solve(Tree* root) {
return isBST(root, INT_MIN, INT_MAX);
}```
```

```                        ```Solution in Python :

# class Tree:
#     def __init__(self, val, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
def solve(self, root):
def inorder(root):
if root is None:
return True
nonlocal l
left = inorder(root.left)
if (l > root.val) or not left:
return False
l = root.val
return inorder(root.right)

l = -float("inf")
return inorder(root)```
```

## Array Manipulation

Starting with a 1-indexed array of zeros and a list of operations, for each operation add a value to each of the array element between two given indices, inclusive. Once all operations have been performed, return the maximum value in the array. Example: n=10 queries=[[1,5,3], [4,8,7], [6,9,1]] Queries are interpreted as follows: a b k 1 5 3 4 8 7 6 9 1 Add the valu

## Print the Elements of a Linked List

This is an to practice traversing a linked list. Given a pointer to the head node of a linked list, print each node's data element, one per line. If the head pointer is null (indicating the list is empty), there is nothing to print. Function Description: Complete the printLinkedList function in the editor below. printLinkedList has the following parameter(s): 1.SinglyLinkedListNode

## Insert a Node at the Tail of a Linked List

You are given the pointer to the head node of a linked list and an integer to add to the list. Create a new node with the given integer. Insert this node at the tail of the linked list and return the head node of the linked list formed after inserting this new node. The given head pointer may be null, meaning that the initial list is empty. Input Format: You have to complete the SinglyLink