19.Remove-Nth-Node-From-End-of-List.py

# https://leetcode.com/problems/remove-nth-node-from-end-of-list/description/
#
# algorithms
# Medium (33.7%)
# Total Accepted:    288.4K
# Total Submissions: 856.2K
# beats 99.78% of python submissions


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

class Solution(object):
    def removeNthFromEnd(self, head, n):
        """
        :type head: ListNode
        :type n: int
        :rtype: ListNode
        """
        if not head:
            return None

        res = ListNode(-1)
        res.next = head

        slow, fast = res, res

        for _ in xrange(n):
            fast = fast.next

        while fast.next:
            fast = fast.next
            slow = slow.next

        slow.next = slow.next.next

        return res.next