92. Reverse Linked List II

题意： Reverse a linked list from position m to n. Do it in-place and in one-pass.

For example:

Given 1->2->3->4->5->NULL, m = 2 and n = 4,return 1->4->3->2->5->NULL.

Note:

Given m, n satisfy the following condition:1 ≤ m ≤ n ≤ length of list. 

思路：就是把中间部分翻转，再把两边连接上

代码：

class Solution(object):    def reverseBetween(self, head, m, n):        """        :type head: ListNode        :type m: int        :type n: int        :rtype: ListNode        """        h = ListNode(0)        h.next = head        p, cnt = h, 1        while 1:            if cnt < m:                p = p.next            elif cnt == m:                t = q = p.next                p.next = None            elif cnt <= n+1:                r = q.next                q.next = p.next                p.next = q                q = r            else:                t.next = q                break            cnt += 1        return h.next