Remove Nth Node From End of List.py

class Solution:
    def removeNthFromEnd(self, head, n):
        fast, slow, prev = head, head, None
        while n > 0:
            fast, n = fast.next, n - 1
        while fast != None:
            fast, slow, prev = fast.next, slow.next, slow
        if prev == None:
            return head.next
        prev.next = prev.next.next
        return head