SDE - 1

You are given an array of integers 'ARR' of length 'N' and an integer Target. Your task is to return all pairs of elements such that they add up to Target.

Note:

We cannot use the element at a given index twice.

Follow Up:

Try to do this problem in O(N) time complexity. 

Given a binary tree with 'N' number of nodes, convert it to a Greater Tree such that data of every node of the original BST is changed to the original node’s data plus the sum of all node’s data greater than or equal to the original data of the node in the BST.

A binary search tree (BST) is a binary tree data structure that 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:

Because only 5 is greater than 4 in the above BST, node 4 will be updated to 9 (4 + 5 = 9).

Nodes 3, 4, and 5 are greater than 2, hence node 2 will be modified to 14 (2 + 3 + 4 + 5 = 14). 

Node with data 5 will remain the same because there is no node in the BST with data greater than 5.

Nodes 2,3, 4, and 5 are greater than 1, hence node 1 will be modified to 15 (1 + 2 + 3 + 4 + 5 = 15).   

Nodes 4 and 5 are greater than 3, hence node 3 will be modified to 12 (3 + 4 + 5 = 12). 

Reverse a given stack of 'N' integers using recursion. You are required to make changes in the input parameter itself.

Note: You are not allowed to use any extra space other than the internal stack space used due to recursion.

Example:

Input: [1,2,3,4,5] 
Output: [5,4,3,2,1]

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