What is the optimal time complexity of solving Reorder List?

The optimized solution achieves a time complexity of O(n) by using sorting, mathematical shortcuts, or hash table lookups.

What is the auxiliary space complexity for Reorder List?

The space complexity is O(1) since we only use a minimal/constant amount of extra memory for tracking variables (or auxiliary space if dynamic structures are allocated).

What are the typical edge cases we must handle in Reorder List?

Key edge cases include empty collections, negative or large bounds causing integer overflow, arrays with only one element, or inputs where target criteria are not met.

How can we optimize the brute force approach for Reorder List?

Brute force methods often inspect all possible combinations. We optimize this by sorting the input list to enable binary search, or tracking processed items in a set to avoid redundant nested loop lookups.

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Reorder List

Learn how to solve the 'Reorder List' problem. This detailed resource details brute force and optimized approaches.

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Problem Statement

Easy

You are given the head of a singly linked list. The list can be represented as:

L0 → L1 → … → Ln-1 → Ln

Reorder the list to be in the following form:

L0 → Ln → L1 → Ln-1 → L2 → Ln-2 → …

You may not modify the values in the list's nodes. Only nodes themselves may be changed.

The linked list is represented as a Python list. Implement a function reorderList(head: list) -> list that returns the reordered list.

Constraints

•The number of nodes in the list is in the range [1, 50000]
•1 <= Node.val <= 1000

Examples

Example 1

Input

[1,2,3,4]

Output

[1,4,2,3]

Explanation

The list 1->2->3->4 is reordered to 1->4->2->3.

Example 2

Input

[1,2,3,4,5]

Output

[1,5,2,4,3]

Explanation

The list 1->2->3->4->5 is reordered to 1->5->2->4->3.

Need a Hint?

Analyze the input constraints. Try sorting first (O(n log n)) or using a hash map/set to track seen elements in O(n) time.

Edge Cases to Watch

Empty list or null input variables
Single item lists/arrays
Extremely large input bounds causing integer or stack overflow

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