109. Reorder List

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Input: head = [1,2,3,4]

Output: [1,4,2,3]

Explanation: The linked list is reordered to alternate between the first and last elements.

Input: head = [1,2,3,4,5]

Output: [1,5,2,4,3]

Explanation: The linked list is reordered to alternate between the first and last elements.

Time Complexity

O(n)

Space Complexity

O(1)