Given a circular linked list, implement an algorithm which returns node at the beginning of the loop.
DEFINITION
Circular linked list: A (corrupt) linked list in which a node’s next pointer points to an earlier node, so as to make a loop in the linked list.
EXAMPLE
Input: A -> B -> C -> D -> E -> C [the same C as earlier]
Output: C
参考：
http://www.cnblogs.com/jdflyfly/p/3829483.html
http://www.cnblogs.com/jdflyfly/p/3829499.html
Cracking the Coding Interview Q2.6,布布扣,bubuko.com
Cracking the Coding Interview Q2.6
原文：http://www.cnblogs.com/jdflyfly/p/3830697.html