2019-06-10 剑指 反转链表

加入哑结点
1对空指针没有特殊处理
10min，和原来写的一模一样

class Solution:
    # 返回ListNode
    def ReverseList(self, pHead):
        # write code here
        if pHead==None:return pHead
        dead = ListNode(None)
        dead.next = pHead
        cur = pHead
        pre = dead
        while(cur!=None):
            next=cur.next
            cur.next=pre
            pre=cur
            cur=next
        pHead.next=None
        return pre

不加入哑结点，代码更简洁，但是不好理解

class Solution:
    # 返回ListNode
    def ReverseList(self, pHead):
        # write code here
        pre=None
        cur=None
        while pHead!=None:
            cur=pHead
            pHead=pHead.next
            cur.next=pre
            pre=cur
        return cur

递归的解法，一次通过。8min

class Solution:
    # 返回ListNode
    def ReverseList(self, pHead):
        # write code here
        if pHead==None:return None #特殊情况
        if pHead.next==None:return pHead #边界情况
        next=pHead.next
        res=self.ReverseList(pHead.next)
        next.next=pHead
        pHead.next=None
        return res