19.Remove Nth Node From End of List

Given a linked list, remove the_n_thnode from the end of list and return its head.

For example,

   Given linked list: 1->2->3->4->5, and n = 2.

   After removing the second node from the end, the linked list becomes 1->2->3->5.

Note:
Given_n_will always be valid.
Try to do this in one pass.

Analyse:

Solution:

class Solution
{