SDE - 2

You are given an integer ‘N’, you need to find whether it’s a good number or not.

We start from the integer ‘N’ and keep replacing the current number with the sum of squares of its digits, we keep repeating this process until we will the number 1. A number that generates the 1 after finite repetition of the above process is called a good number.

Example :

If ‘N’ = 7,

Then we start with the integer 7 and replace it with (7 * 7) = 49.
The new number is 49, we replace it with (4 * 4) + (9 * 9) = 97.
We replace this new number 97 with (9 * 9) + (7 * 7) = 130.
We replace this new number 130 with (1 * 1) + (3 * 3) + (0 * 0) = 10.
We replace this new number 10 with (1 * 1) + (0 * 0) = 1.

Therefore, the original number 7 is a good number. 

You are given an array/list ‘ARR’ of ‘N’ positive integers where each element describes the length of the stick. You have to connect all sticks into one. At a time, you can join any two sticks by paying a cost of ‘X’ and ‘Y’ where ‘X’ is the length of the first stick and ‘Y’ is the length of the second stick and the new stick we get will have a length equal to (X+Y). You have to find the minimum cost to connect all the sticks into one.

You are given a Binary Search Tree (BST) and a target value ‘K’. Your task is to return true if there exist two nodes in the given BST such that the sum of their values is equal to the given target ‘K’, else return false.

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.

Note:

1. All the elements of the Binary Search Tree are unique.

2. You can’t use the same node value/element of BST twice.

For example:

tree: 8 5 10 2 6 -1 -1 -1 -1 -1 7 -1 -1
'K' = 13,

The nodes with values 8 and 5 as shown in the above figure gives sum equal to the given target 13. 

Therefore, the output will be “true” i.e it is possible to find a pair in the given BST having sum equal to ‘K’.

Ninja is given an array of integers that contain numbers in random order. He needs to write a program to find and return the number which occurs the maximum times in the given input. He needs your help to solve this problem.

If two or more elements contend for the maximum frequency, return the element which occurs in the array first i.e. whose index is lowest.

For example,

For 'arr' = [ 1, 2, 3, 1, 2]. you need to return 1.

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