Linked List and Binary Tree Ops | Dataford Interview Questions

The Zeta mobile app stores a user's activity feed as a singly linked list. Given the head of the list, reverse the list in place and return the new head so the feed displays the newest node first.

Formal Specification

Implement reverse_list(head):

Input: head, either None or a reference to the first ListNode in a singly linked list. Each node has integer field val and pointer field next.
Output: The new head after reversing every next pointer. The original nodes must be reused, and no new list nodes may be created.
The test representation uses an array of values. For example, [1, 2, 3] represents 1 -> 2 -> 3.

Constraints

0 <= number of nodes <= 10^5
-10^9 <= node.val <= 10^9
The list contains no cycles
No new list nodes may be created

Function Signature

def reverse_list(head):

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