循环反转单链表

class ListNode:
    def __init__(self,x):
        self.val = x
        self.next = None

def list_reverse(head):
    if head is None or head.next is None:
        return head
    pre = None
    cur = head
    h = head
    while cur:
        h = cur
        tmp = cur.next
        cur.next = pre
        pre = cur
        cur = tmp
    return h

递归实现单链表反转

class ListNode:
    def __init__(self,x):
        self.val = x
        self.next = None

def recurse(head,newhead):
    if head is None:
        return
    if head.next is None:
        newhead = head
    else:
        newhead = recurse(head.next,newhead)
        head.next.next = head
        head.next = None
    return newhead