Linked List Reordering Practice | Dataford Interview Questions

Meta IT maintains a singly linked list of related service links. Reorder the list in place so the sequence becomes L0 -> Ln -> L1 -> Ln-1 -> L2 -> Ln-2 -> ....

Implement reorder_list(head). The function receives the head of a singly linked list and must modify the existing nodes without creating replacement nodes. Return the same head node after reordering.

Formal Specification

Input: head, a ListNode object or None. Each node has an integer val and a next pointer.
Output: The original head node, with its links rearranged in the required order.
The test harness represents a linked list as an array of values. For example, [1, 2, 3] represents 1 -> 2 -> 3.

Constraints

0 <= number of nodes <= 5 * 10^4
-10^5 <= node.val <= 10^5
Use O(1) auxiliary space
Do not allocate new list nodes

Function Signature

def reorder_list(head):

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