LeetCode 206. 反转链表

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode* res = new ListNode(0);
        ListNode* temp = NULL;

        while (head) {
            temp = head ->next;
            head ->next = res ->next;
            res ->next = head;
            head = temp;
        } 

        return res ->next;
    }
};