SDE - 2

You have a 2D grid of ‘N’ rows and ‘M’ columns which are initially filled with water. You are given ‘Q’ queries each consisting of two integers ‘X’ and ‘Y’ and in each query operation, you have to turn the water at position (‘X’, ‘Y’) into a land. You are supposed to find the number of islands in the grid after each query.

An island is a group of lands surrounded by water horizontally, vertically, or diagonally.

You are given a Singly Linked List of N nodes such that each node represents a single digit.

Your task is to return a node 'X', where 'X' represents the head of the Linked List storing the digits of the sum(most significant digit at the head) formed by adding the 1st half and 2nd half of the given Linked List.

Note:

1. When N is odd consider the middle element to be part of 1st half.

2. The sum should not contain any leading zero, except the number 0 itself.

For Example:

Given Linked List: 1-2-3-4-5-5-6

First half: 1-2-3-4    
Second half: 5-5-6

Output Linked List: 1-7-9-0 = (1234 + 556 = 1790)

Follow Up:

Can you add both halves without finding the length of Linked List and in O(1) space?

You are given an array 'a' of size 'n'.

Print the Next Greater Element(NGE) for every element.

The Next Greater Element for an element 'x' is the first element on the right side of 'x' in the array, which is greater than 'x'.

If no greater elements exist to the right of 'x', consider the next greater element as -1.

For example:

Input: 'a' = [7, 12, 1, 20]

Output: NGE = [12, 20, 20, -1]

Explanation: For the given array,

- The next greater element for 7 is 12.

- The next greater element for 12 is 20. 

- The next greater element for 1 is 20. 

- There is no greater element for 20 on the right side. So we consider NGE as -1.

You are given a list of “N” strings A. Your task is to check whether you can form a given target string using a combination of one or more strings of A.

Note :

You can use any string of A multiple times.

Examples :

A =[“coding”, ”ninjas”, “is”, “awesome”]  target = “codingninjas”
Ans = true as we use “coding” and “ninjas” to form “codingninjas”

You are given an integer 'N', your task is to generate all combinations of well-formed parenthesis having ‘N’ pairs.

A parenthesis is called well-formed if it is balanced i.e. each left parenthesis has a matching right parenthesis and the matched pairs are well nested.

For Example:

For ‘N’ = 3,
All possible combinations are: 
((()))
(()())
(())()
()(())
()()()

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