翻转链表

35. 翻转链表

翻转一个链表

样例

给出一个链表1->2->3->null，这个翻转后的链表为3->2->1->null

挑战

在原地一次翻转完成

/**
 * Definition of singly-linked-list:
 *
 * class ListNode {
 * public:
 *     int val;
 *     ListNode *next;
 *     ListNode(int val) {
 *        this->val = val;
 *        this->next = NULL;
 *     }
 * }
 */

class Solution {
public:
    /**
     * @param head: n
     * @return: The new head of reversed linked list.
     */
    ListNode * reverse(ListNode * head) {
        // write your code here
        if(head==NULL) return head;
        ListNode* res=NULL;
        while(head!=NULL)
        {
            ListNode* node=head->next;
            head->next=res;
            res=head;
            head=node;
        }
        return res;
    }
};

"""
Definition of ListNode

class ListNode(object):

    def __init__(self, val, next=None):
        self.val = val
        self.next = next
"""

class Solution:
    """
    @param head: n
    @return: The new head of reversed linked list.
    """
    def reverse(self, head):
        # write your code here
        if head==None:
            return head
        res=None;
        while head!=None:
            node=head.next;
            head.next=res;
            res=head;
            head=node;
        return res;