Leetcode 206: Reversed Linked List

https://leetcode.com/problems/reverse-linked-list/

Code (Iterative)

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if head is None:
            return None
            
        next_node = head.next
        head.next = None
        
        while next_node is not None:
            next_next_node = next_node.next
            next_node.next = head
            head = next_node
            next_node = next_next_node
        
        return head

 

Code (Recursive)

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class Solution(object):
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if head is None or head.next is None:
            return head
        
        next_node = head.next
        new_head = self.reverseList(next_node)
        head.next = None
        next_node.next = head

        return new_head