206_Reverse_Linked_List.py

"""
206. Reverse Linked List

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

"""

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
        prev = None
        curr = head
        while curr:
            upcoming = curr.next
            curr.next = prev
            prev = curr
            curr = upcoming
        
        return prev