/**
* Definition of singly-linked-list:
*
* class ListNode {
* public:
* int val;
* ListNode *next;
* ListNode(int val) {
* this->val = val;
* this->next = NULL;
* }
* }
*/
///递归方法
class Solution {
public:
/**
* @param head: n
* @return: The new head of reversed linked list.
*/
ListNode * reverse(ListNode * head) {
// write your code here
if(head == NULL || head->next == NULL) return head;//先将头节点与最后一个节点翻转
ListNode* r = reverse(head->next);
head->next->next = head;//头节点以外的节点所以是把next的和next.next的翻转
head->next = NULL;//头节点被转到最后一位 下一个为null
return r;
}
};
///循环方法
class Solution {
public:
/**
* @param head: n
* @return: The new head of reversed linked list.
*/
ListNode * reverse(ListNode * head) {
if (head == NULL) {
return NULL;
}
ListNode *per = NULL, *cur = head, *net = head->next;
while (net != NULL) {
cur->next = per;
per = cur;
cur = net;
net = cur->next;
}
cur->next = per;
return cur;
}
};
