Tech Analyst

You have been given a binary tree of integers with N number of nodes. Your task is to check if that input tree is a BST (Binary Search Tree) or not.

A binary search tree (BST) is a binary tree data structure which has the following properties.

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

Example :

Answer :

Level 1: 

All the nodes in the left subtree of 4 (2, 1, 3) are smaller 
than 4, all the nodes in the right subtree of the 4 (5) are 
larger than 4.

Level 2 :

For node 2:
All the nodes in the left subtree of 2 (1) are smaller than 
2, all the nodes in the right subtree of the 2 (3) are larger than 2.
For node 5:
The left and right subtrees for node 5 are empty.

Level 3:

For node 1:
The left and right subtrees for node 1 are empty.
For node 3:
The left and right subtrees for node 3 are empty.

Because all the nodes follow the property of a binary search tree, the above tree is a binary search tree.

You are given a sorted array 'A' of length 'N', two integers 'K' and 'X'. Your task is to print 'K' integers closest to 'X', if two integers are at the same distance return the smaller one.

The output should also be in sorted order

Note:

An integer 'a' is closer to 'X' than an integer 'b' if: 
|a - X| < |b - X|  or (  |a - X| == |b - X| and a < b )

For Example:

if X = 4,  3 is closer to 'X' than 9, as |3-4| < |9-4|  i.e., 1 < 5   and if X = 4, 2 and 6 are equally close to it, as |2-4| == |6-4| = 2, but we say 2 is closer to 4 than 6, as 2 is smaller.

You are given an array/list 'ARR' of integers of length ‘N’. You are supposed to find all the elements that occur strictly more than floor(N/3) times in the given array/list.

You are given an integer ‘N’, you need to find the count of binary strings of length equal to ‘N’ that do not contain consecutive 1’s. As the answer can be large, print its value modulo 10^9 + 7.

Follow up :

Can you try to solve this problem in O(N) time and O(1) space?

Example :

If ‘N’ = 3

Then there are 5 possible binary strings of length equal to 3 that do not contain consecutive 1’s: “000”, “001”, “010”, “100”, “101”.

You have been given a text message. You have to return the Run-length Encoding of the given message.

Run-length encoding is a fast and simple method of encoding strings. The basic idea is to represent repeated successive characters as the character and a single count. For example, the string "aaaabbbccdaa" would be encoded as "a4b3c2d1a2".

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You are given the root node of a binary tree consisting of ‘N’ nodes. Your task is to return its preorder traversal. The preorder traversal of a binary tree is defined as a process of traversing each node in the following manner-:

1- Visit the root node.
2- Traverse all nodes in the left subtree of the root node.
3- Traverse all the nodes in the right subtree of the root node.

For Example:

For the given tree below,
Preorder traversal for the given tree will be [1, 2, 4, 5, 3]. Hence, the answer is [1, 2, 4, 5, 3].

Example:

Elements are in the level order form. The input consists of values of nodes separated by a single space in a single line. In case a node is null, we take -1 in its place.

For example, the input for the tree depicted in the below image would be :

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

Explanation :
Level 1 :
The root node of the tree is 1

Level 2 :
Left child of 1 = 2
Right child of 1 = 3

Level 3 :
Left child of 2 = 4
Right child of 2 = null (-1)
Left child of 3 = 5
Right child of 3 = 6

Level 4 :
Left child of 4 = null (-1)
Right child of 4 = 7
Left child of 5 = null (-1)
Right child of 5 = null (-1)
Left child of 6 = null (-1)
Right child of 6 = null (-1)

Level 5 :
Left child of 7 = null (-1)
Right child of 7 = null (-1)

The first not-null node (of the previous level) is treated as the parent of the first two nodes of the current level. 

The second not-null node (of the previous level) is treated as the parent node for the next two nodes of the current level and so on.

The input ends when all nodes at the last level are null (-1).

Note :

The above format was just to provide clarity on how the input is formed for a given tree. 

The sequence will be put together in a single line separated by a single space. Hence, for the above-depicted tree, the input will be given as:

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

Given an array ‘arr’ of size ‘n’ find the largest element in the array.

Example:

Input: 'n' = 5, 'arr' = [1, 2, 3, 4, 5]

Output: 5

Explanation: From the array {1, 2, 3, 4, 5}, the largest element is 5.

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1 low level design question to design a parking lot.