链表反转

 

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if not head:
            return head
        else:
            '''
            p = head
            q = head.next
            p.next = None
            n=0
            while q:
                r = q.next
                q.next = p
                p = q
                q = r
            return p
            '''
            l = []
            while head != None:
                l.append(head.val)
                head = head.next
            l.reverse()
            res = ListNode(l[0])
            r = res
            for i in range(1,len(l)):
                res1 = ListNode(l[i])
                res.next = res1
                res = res.next
            return r