Implement an algorithm to find the kth to last element of a singly linked list.
思路：双指针
参考 http://www.cnblogs.com/jdflyfly/p/3810697.html
Cracking the Coding Interview Q2.2,布布扣,bubuko.com
Cracking the Coding Interview Q2.2
原文地址：http://www.cnblogs.com/jdflyfly/p/3830639.html
