SDE - 1

Ninja loves playing with numbers. So one day, he wants to arrange a few numbers in the ‘N’ number of rows. The first row contains 1 number, the second row has two numbers, the third row has 4 numbers, and so on.

Ninja starts placing numbers in increasing order, with absolute difference 1, starting from 1 and continuing till he encounters 9, and then he again restarts from 1.

You are given an integer ‘N’ denoting the given number of rows. Can you print the pattern Ninja wants to create?

Pattern for N = 4:

1
23
4567
89123456

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 an array of distinct elements, and you have to rearrange the array elements in a zig-zag fashion. In other words, for every odd position ‘i’ in the array 'ARR,' 'ARR'[i] should be greater than 'ARR'[i-1] and 'ARR'[i] should be greater than 'ARR'[i+1].

For example:

Given ‘N’ = 4, 
'ARR' = { 4, 3, 2, 1} 
Then a possible array is 3, 4, 1, 2.

Note:

You are supposed to return the array, which is in a zig-zag fashion.

Since there can be multiple answers for a particular array, any of the possible solutions are accepted.

It can be proved. A zig-zag array is always possible for a given array.

You are given a linked list containing 'n' 'head' nodes, where every node in the linked list contains two pointers:

(1) ‘next’ which points to the next node in the list

(2) ‘child’ pointer to a linked list where the current node is the head.

Each of these child linked lists is in sorted order and connected by 'child' pointer.

Your task is to flatten this linked such that all nodes appear in a single layer or level in a 'sorted order'.

Input: Given linked list is:

Output:
1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → 9 → 12 → 20 → null.


Explanation:
The returned linked list should be in a sorted order. All the elements in this returned linked list are connected by 'child' pointers and 'next' pointers point to null.

You are given a 2-dimensional array/list having N rows and M columns, which is filled with ones(1) and zeroes(0). 1 signifies land, and 0 signifies water.

A cell is said to be connected to another cell, if one cell lies immediately next to the other cell, in any of the eight directions (two vertical, two horizontal, and four diagonals).

A group of connected cells having value 1 is called an island. Your task is to find the number of such islands present in the matrix.