Reverse a singly-linked list recursively.
Examples
L = null, return null
L = 1 -> null, return 1 -> null
L = 1 -> 2 -> 3 -> null, return 3 -> 2 -> 1 -> null
class Solution(object):
def reverse(self, head):
return self._reverse(head)
def _reverse(self, node, prev=None):
if not node:
return prev
n = node.next
node.next = prev
return self._reverse(n, node)
