Linked List Reversal With Pointers | Dataford Interview Questions

An EPAM Systems data-processing component stores an ordered sequence as a singly linked list. Given the list head, reverse the list in place by changing node pointers, then return the new head.

Formal Specification

The input is head, either None or a reference to a ListNode with integer field val and pointer field next. The evaluator supplies the ListNode implementation. Return a reference to the new head after every next pointer has been reversed. Do not create replacement nodes or use an array to rebuild the list.

For test cases below, a JSON array represents the linked list's values. The expected result is the value sequence obtained by traversing the returned head.

Constraints

0 <= n <= 10^5
-10^9 <= node.val <= 10^9
The list contains no cycles
Do not allocate replacement nodes
Use O(1) auxiliary space

Function Signature

def reverse_linked_list(head):

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