0206: Reverse Linked List

Problem Statement

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

Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?

Code Solution

class Solution:
    def reverseList(self, head):
	    
        def rev(node):
            prev = None
            curr = node
            while curr:
                temp = curr.next
                curr.next = prev
                prev = curr
                curr = temp
            return prev
        
        return rev(head)