Reverse Linked List (Iterative)

Given the head of a singly linked list, reverse the list, and return the reversed list. Example: Input: head = [1,2,3,4,5] Output: [5,4,3,2,1] Explanation: The list is reversed end-to-end. Pattern focus: In-Place Reversal (iterative using dummy or two pointers).

Input Format

head = ListNode

Output Format

return ListNode

Constraints

  • The number of nodes is in the range [0, 5000].
  • -5000 <= Node.val <= 5000

Examples

Example 1:

Input:

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

Output:

[5,4,3,2,1]

Explanation:

All pointers reversed; tail becomes new head.

Example 2:

Input:

head = []

Output:

null

Explanation:

Empty list stays empty.

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Reverse Linked List (Iterative) - Linked List