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Reverse Linked List

Moderate
0/80
Average time to solve is 15m
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Contributed by
469 upvotes
Asked in companies
CognizantMicrosoftSAP Labs

Problem statement

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?
Detailed explanation ( Input/output format, Notes, Images )
Constraints :
1 <= T <= 5
0 <= L <= 10^5
1 <= data <= 10^9 and data != -1

Time Limit: 1 sec
Sample Input 1 :
1
1 2 3 4 5 6 -1
Sample Output 1 :
6 5 4 3 2 1 -1
Explanation For Sample Input 1 :
For the first test case,  After changing the next pointer of each node to the previous node, The given linked list is reversed.
Sample Input 2 :
1
10 21 3 2 4 -1
Sample Output 2 :
4 2 3 21 10 -1
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