Leetcode[206]-Reverse Linked List

Reverse a singly linked list.Reverse a singly linked list.

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

分析：

/**
 * 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;
        if(head == NULL || head->next==NULL) return head;

        pre= head->next;

        head->next = NULL;
        while(pre!=NULL){
            ListNode * nextNode = NULL;
            nextNode = pre->next;
            pre->next = head;
            head = pre;
            pre = nextNode;
            delete nextNode;
        }
        delete pre;
        return head;
    }
};