In this Reverse a doubly linked list HackerRank solution, 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):
- DoublyLinkedListNode head: a reference to the head of a DoublyLinkedList
Returns
– DoublyLinkedListNode: a reference to the head of the reversed list
Input Format
The first line contains an integer , the number of test cases.
Each test case is of the following format:
- The first line contains an integer , the number of elements in the linked list.
- The next lines contain an integer each denoting an element of the linked list.
Constraints
Output Format
Return a reference to the head of your reversed list. The provided code will print the reverse array as a one line of space-separated integers for each test case.
Sample Input
1
4
1
2
3
4
Sample Output
4 3 2 1
Explanation
The initial doubly linked list is:
The reversed doubly linked list is:
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):
- DoublyLinkedListNode head: a reference to the head of a DoublyLinkedList
Returns
– DoublyLinkedListNode: a reference to the head of the reversed list
Input Format
The first line contains an integer , the number of test cases.
Each test case is of the following format:
- The first line contains an integer , the number of elements in the linked list.
- The next lines contain an integer each denoting an element of the linked list.
Constraints
Output Format
Return a reference to the head of your reversed list. The provided code will print the reverse array as a one line of space-separated integers for each test case.
Sample Input
1
4
1
2
3
4
Sample Output
4 3 2 1
Reverse a doubly linked list HackerRank solution
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Problem Solution in Python
def reverse(llist):
# Write your code here
if llist == None or llist.next == None:
return llist
while llist != None:
nxt = llist.next
llist.next = llist.prev
llist.prev = nxt
if nxt is None: break
llist = nxt
return llistProblem Solution in Java
public static DoublyLinkedListNode reverse(DoublyLinkedListNode llist) {
// Write your code here
DoublyLinkedListNode prev = null;
DoublyLinkedListNode next = null;
DoublyLinkedListNode current = llist;
while(current!=null){
next = current.next;
current.next = prev;
current.prev = next;
prev = current;
current = next;
}
current = prev;
return current;
}