Reverse Linked List

206. Reverse Linked List

Solutions

1. Solution 1: Iterative

   def reverseList(self, head):
    """
    :type head: ListNode
    :rtype: ListNode
    """
    if head == None:
        return head
    next = head.next
    last = None
    while head!=None:
        tmp = head.next
        head.next = last
        last = head
        head = tmp
       
    return last
   

2. Solution 2: Recursive

   def reverseList(self, head):
    """
    :type head: ListNode
    :rtype: ListNode
    """
    def reverse(prev, curr):
        if curr == None:
            return prev
        else:
            tmp = curr.next
            curr.next = prev
            return reverse(curr, tmp)
           
    return reverse(None, head)