chapter 2 Linked List

1. remember that when you're discussing a linked list in an interview, you must understand whether it is a singly linked list or a doubly linked list.

2. deleting a node from a singly linked list, the important things to remember are (1) to check for the null pointer and (2) to update the head or tail pointer as necessary.

3. the runner technique is used in many linked list problems. 一个快指针一个慢指针， 快指针可以有fixed amount steps。 例如啊a1->a2->a3->a4->b1->b2->b3->b4变成a1->b1->a2->b2->a3->b3->a4->b4 快指针每次比慢指针多走一步，等到快指针到末尾，慢指针在中间，然后快指针再次指向head，这样就可以操作了