python 实现链表的反转

从头开始遍历，每一个节点的next指向它的前一个节点。

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class ListNode:
    def __init__(self,x):
        self.val=x
        self.next=None
        
def nonrecurse(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
        
head = ListNode(1)
p1=ListNode(2)
p2=ListNode(3)
p3=ListNode(4)
head.next = p1
p1.next = p2
p2.next = p3
p=nonrecurse(head)
while p:
    print p.val
    p=p.next


        
head = ListNode(1)
p1=ListNode(2)
p2=ListNode(3)
p3=ListNode(4)
head.next = p1
p1.next = p2
p2.next = p3
p=nonrecurse(head)
while p:
    print p.val
    p=p.next