206. Reverse Linked List

Easy

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

Solution

class Solution:
    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
        prev = None
        curr = head
        next = None

        while curr is not None:
            next = curr.next
            curr.next = prev
            prev = curr
            curr = next

        return prev


class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next