leetcode:206 Reverse Linked List－每日編程第十四題

Reverse Linked List

Total Accepted: 65133 Total Submissions: 179691 Difficulty: Easy

Reverse a singly linked list.

Hint:

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

 

非遞歸：

 /**
  * Definition for singly-linked list.
  * struct ListNode {
  *     int val;
  *     ListNode *next;
  *     ListNode(int x) : val(x), next(NULL) {}
  * };
  */
 class Solution {
 public:
     ListNode* reverseList(ListNode* head) {
         ListNode* pre = NULL;
         ListNode* next;
         while(head!=NULL){
             next=head->next;
             head->next=pre;
             pre=head;
             head=next;
         }
         return pre;
     }
 };

遞歸：

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode* reverseList(ListNode* head) {
12         if(head==NULL){
13             return NULL;
14         }
15         if(head->next==NULL){
16             return head;
17         }else{
18             ListNode* tem=reverseList(head->next);
19             head->next->next=head;
20             head->next=NULL;
21             return tem;
22         }
23         
24     }
25 };