LeetCode 筆記 - 206. Reverse Linked 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]:
        
        def walk(last, current) -> Optional[ListNode]:
            if current is None:
                return last
            
            next_temp = current.next
            current.next = last
            
            return walk(current, next_temp)
        return walk(None, head)