### Reversing first k nodes of a Linked List

In this post, we will discuss a method to reverse k nodes from the starting of the linked list. In one of my earlier post, we have already discussed methods to reverse a given linked list. Here We will create a method that accepts the head of the linked list and Number k that indicates the number of elements to be reversed. To do this we will be using a simple method to reverse the linked list with an additional condition in the while loop where decrease k after each iteration. Have a look at my previous post on Linked List in c++ to see how to reverse a linked list.

Let’s directly look at the algorithm and code to understand it better

Algorithm:

1. In the above code, we use 3 pointers current, previous and next
2. Initially, the current node points to the head node, the previous and next nodes are Null
3. Then we use a while loop to traverse through the linked list and also decrease k
4. In each iteration, we do the following
• assign next pointer to current node's link field
• update current nodes link field to point to the previous node
• update the previous node to point to the current node
• when k is 0 then previous node points to the starting of the linked list so we assign it to the head node
5. We also need to join the link between the current node and the next node

Suggestion: To understand the algorithm and its working better try doing a dry run on the paper by considering a simple linked list.

### Sample input and output to check the program

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NOTE: This changes one thing that is instead of encountering the opening bracket we now first encounter the closing bracket and we make changes accordingly in our code.

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Hashing is a technique used for storing , searching and removing elements in almost constant time. Hashing is done with help of a hash function that generates index for a given input, then this index can be used to search the elements, store an element, or remove that element from that index.

A hash function is a function that is used to map the data elements to their position in the data structure used. For example if we use an array to store the integer elements then the hash function will generate position for each element so that searching, storing and removing operation on the array can be done in constant time that is independent of the number of elements in the array. For better look at the example below.

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