0206-reverse-linked-list.rb

# frozen_string_literal: true

# 206. Reverse Linked List
# https://leetcode.com/problems/reverse-linked-list

=begin

Given the head of a singly linked list, reverse the list, and return the reversed list.

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

### Example 2:
Input: head = [1,2]
Output: [2,1]

### Example 3:
Input: head = []
Output: []

### Constraints:
* The number of nodes in the list is the range [0, 5000].
* -5000 <= Node.val <= 5000

=end

# Definition for singly-linked list.
# class ListNode
# attr_accessor :val, :next
# def initialize(val = 0, _next = nil)
# @val = val
# @next = _next
# end
# end
# @param {ListNode} head
# @return {ListNode}
defreverse_list(head,prev=nil)
whilehead
head,head.next,prev=head.next,prev,head
end
prev
end