104. Reverse a Linked List

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

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

Explanation: The original list 1->2->3->4->5 is reversed to 5->4->3->2->1.

Input: head = [1,2]

Output: [2,1]

Explanation: The original list 1->2 is reversed to 2->1.

Input: head = []

Output: []

Explanation: An empty list remains empty after reversal.

Time Complexity

O(n)

Space Complexity

O(1)