# Reverse a doubly linked list

### Problem Statement :

```This challenge is part of a tutorial track by MyCodeSchool

Given the pointer to the head node of a doubly linked list, reverse the order of the nodes in place. That is, change the next and prev pointers of the nodes so that the direction of the list is reversed. Return a reference to the head node of the reversed list.

Note: The head node might be NULL to indicate that the list is empty.

Function Description

Complete the reverse function in the editor below.

reverse has the following parameter(s):

Returns

Input Format

The first line contains an integer t, the number of test cases.

Each test case is of the following format:

The first line contains an integer n, the number of elements in the linked list.
The next n lines contain an integer each denoting an element of the linked list.```

### Solution :

```                            ```Solution in C :

In C++ :

/*
Reverse a doubly linked list, input list may also be empty
Node is defined as
struct Node
{
int data;
Node *next;
Node *prev
}
*/
{
// Complete this function
// Do not write the main method.

Node *temp = NULL;

/* swap next and prev for all nodes of
while (current !=  NULL)
{
temp = current->prev;
current->prev = current->next;
current->next = temp;
current = current->prev;
}

/* Before changing head, check for the cases like empty
list and list with only one node */
if(temp != NULL )

}

In Java :

/*
Insert Node at the end of a linked list
head pointer input could be NULL as well for empty list
Node is defined as
class Node {
int data;
Node next;
Node prev;
}
*/

return null;

Node next=temp.next;
while(next!=null)
{

temp.next=temp.prev;
temp.prev=next;
temp=next;
next=next.next;

}

temp.next=temp.prev;
temp.prev=null;
return temp;

}

In python3 :

while curr.next != None:
prev, curr = curr, curr.next

while prev != None:
curr.prev = curr.next
curr.next = prev
prev.next = prev.prev
prev.prev = curr
prev, curr = prev.next, prev

In C :

// Complete the reverse function below.

/*
*
*     int data;
* };
*
*/
prev=NULL;
while(curr)
{
next=curr->next;
curr->next=prev;
curr->prev=next;
if(next==NULL)break;
prev=curr;curr=next;
}
curr->prev=NULL;return curr;

}```
```

## No Prefix Set

There is a given list of strings where each string contains only lowercase letters from a - j, inclusive. The set of strings is said to be a GOOD SET if no string is a prefix of another string. In this case, print GOOD SET. Otherwise, print BAD SET on the first line followed by the string being checked. Note If two strings are identical, they are prefixes of each other. Function Descriptio

## Cube Summation

You are given a 3-D Matrix in which each block contains 0 initially. The first block is defined by the coordinate (1,1,1) and the last block is defined by the coordinate (N,N,N). There are two types of queries. UPDATE x y z W updates the value of block (x,y,z) to W. QUERY x1 y1 z1 x2 y2 z2 calculates the sum of the value of blocks whose x coordinate is between x1 and x2 (inclusive), y coor

## Direct Connections

Enter-View ( EV ) is a linear, street-like country. By linear, we mean all the cities of the country are placed on a single straight line - the x -axis. Thus every city's position can be defined by a single coordinate, xi, the distance from the left borderline of the country. You can treat all cities as single points. Unfortunately, the dictator of telecommunication of EV (Mr. S. Treat Jr.) do

## Subsequence Weighting

A subsequence of a sequence is a sequence which is obtained by deleting zero or more elements from the sequence. You are given a sequence A in which every element is a pair of integers i.e A = [(a1, w1), (a2, w2),..., (aN, wN)]. For a subseqence B = [(b1, v1), (b2, v2), ...., (bM, vM)] of the given sequence : We call it increasing if for every i (1 <= i < M ) , bi < bi+1. Weight(B) =