Reverse Linked List

Reverse a singly linked list.

递归或者非递归.
需要注意的是反转后最后节点的next指向(NULL).

/**
* 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) {
/// method 1
// if(head == NULL || head->next == NULL) {
//     return head;
// }

// ListNode* tmp;
// ListNode* p = NULL;
// ListNode* p1 = head;

// while(p1 != NULL) {
//     tmp = p1->next;
//     p1->next = p;
//     p = p1;
//     p1 = tmp;
// }

// head = p;
// return head;

/// method 2
if(head == NULL || head->next == NULL) {
return head;
}
ListNode* p = head->next;
ListNode* temp = reverseList(p);
p->next = head;
head->next = NULL;
return temp;
}
};