【leetcode 链表】206. Reverse Linked List C++

206. Reverse Linked List

/**
 * 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* newHead = new ListNode(0);
        ListNode *p = head, *q = NULL, *t;
        while(p) {
            t = p->next;
            p->next = q;
            newHead->next = p;

            q = p;
            p = t;
        }
        return newHead->next;
    }
};

/**
 * 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 || !head->next) return head;
        ListNode* newHead = reverseList(head->next);
        head->next->next = head;
        head->next = NULL;
        return newHead;
    }
};