SDE - 1

Given a singly linked list of integers. Your task is to return the head of the reversed linked list.

For example:

The given linked list is 1 -> 2 -> 3 -> 4-> NULL. Then the reverse linked list is 4 -> 3 -> 2 -> 1 -> NULL and the head of the reversed linked list will be 4.

Follow Up :

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

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

1. Push(num): Push the given number in the stack.
2. Pop: Remove and return the top element from the stack if present, else return -1.
3. Top: return the top element of the stack if present, else return -1.
4. getMin: Returns minimum element of the stack if present, else return -1.

For Example:

For the following input: 
1
5
1 1
1 2
4
2
3

For the first two operations, we will just insert 1 and then 2 into the stack which was empty earlier. So now the stack is => [2,1]
In the third operation, we need to return the minimum element of the stack, i.e., 1. So now the stack is => [2,1]
For the fourth operation, we need to pop the topmost element of the stack, i.e., 2. Now the stack is => [1]
In the fifth operation, we return the top element of the stack, i.e. 1 as it has one element. Now the stack is => [1]

So, the final output will be: 
1 2 1

A doubly-linked list is a data structure that consists of sequentially linked nodes, and the nodes have reference to both the previous and the next nodes in the sequence of nodes.

You are given a sorted doubly linked list of size 'n'.

Remove all the duplicate nodes present in the linked list.

Example :

Input: Linked List: 1 <-> 2 <-> 2 <-> 2 <-> 3

Output: Modified Linked List: 1 <-> 2 <-> 3

Explanation: We will delete the duplicate values ‘2’ present in the linked list.

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What is a friend function?

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