Reverse Linked List

Reverse a singly linked list.

class Solution(object):
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        pre = None
        while head:
            nxt = head.next
            head.next = pre
            pre = head
            head = nxt
        return pre

注意 开始节点和结尾节点，还有while终止条件