剑指 Offer 24. 反转链表

原题链接：剑指 Offer 24. 反转链表

 

solution:
        直接遍历链表：

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

        递归：
 

/**
 * 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 *tail = reverseList(head->next);
        head->next->next = head;
        head->next = NULL;
        return tail;
    }
};