question 1 :Swap Nodes in Pairs
https://leetcode.cn/problems/swap-nodes-in-pairs/
I was a little confused at first because I'm thinking whether should I creat a new head, but soon I came up with the idea of creat pre = None and with an 'if - else' structure to deal the problem
question 2:Remove Nth Node From End of List
https://leetcode.cn/problems/remove-nth-node-from-end-of-list/
easy
question 3 : Intersection of Two Linked Lists LCCI
https://leetcode.cn/problems/intersection-of-two-linked-lists-lcci/
fine
question 4 :Linked List Cycle II
the question ask to return -1 if there don't exist a cycle, but actually should return 'None'
leetcode 英语版太糟糕了