LeetCode#206 Reverse Linked List

Problem Definition:

　　

Reverse a singly linked list.

Hint:

A linked list can be reversed either iteratively or recursively. Could you implement both?

 

Solution 1:  找到最后一个节点作为起始节点，头插。

def reverseList(head):
        if head==None:
            return head
        tail=head
        while tail.next!=None:
            tail=tail.next
        while head!=tail:
            hn=head.next
            head.next=tail.next
            tail.next=head
            head=hn
        return tail

 

Solution 2: 遍历直接反转。

 1 def reverseList(self, head):
 2         if head==None:
 3             return head
 4         p=head.next
 5         head.next=None
 6         while p!=None:
 7             tmp=p.next
 8             p.next=head
 9             head=p
10             p=tmp
11         return head

Solution 3：递归。把Solution 2的循环改成递归实现。

 1 def reverseList(head):
 2         if head==None:
 3             return head
 4         p=head.next
 5         head.next=None
 6         return recursive(head,p)
 7 def recursive(head,p):
 8         if p==None:
 9             return head
10         tmp=p.next
11         p.next=head
12         return recursive(p,tmp)

 

 

 

 

posted @ 2015-07-17 09:32  曾可爱  阅读(132)  评论(0)    收藏  举报