Reverse a Linked List

easy

A document editor stores its undo history as a singly linked chain, oldest action first. To replay history newest-first, you need the whole chain flipped — in place, no second copy (the chain can be huge).

Given the head of a singly linked list, reverse it and return the new head. Tests pass the list as a plain array; build and serialize handle the conversion — your work happens in _reverse, on real nodes.

Example 1

in values = [1, 2, 3, 4, 5]

out [5, 4, 3, 2, 1]

Example 2

in values = [1, 2]

out [2, 1]

Example 3

in values = []

out []

An empty list reverses to an empty list.

Constraints

· 0 <= number of nodes <= 5000
· -5000 <= node value <= 5000
· O(1) extra space — reverse in place