leetcode 206 反转链表

比较简单的题目

迭代写法:

/**
 * 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,*next=NULL,*cur=head;
        while(cur){
            next=cur->next;
            cur->next=pre;
            //pre->next=next;
            pre=cur;
            cur=next;
        }
        return pre;
    }
};

递归写法:

/**
 * 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) {
        if(head==NULL||head->next==NULL) return head;
        ListNode* newhead=reverseList(head->next);
        head->next->next=head;
        head->next=NULL;
        return newhead;
    }
};