LeetCode 206. Reverse Linked List

Reverse a singly linked list.

click to show more hints.

Hint:
A linked list can be reversed either iteratively or recursively. Could you implement both?
一，算法分析
头插法重建单链表，注意默认链表是没有头结点的，所以建表的时候不断更新head节点；Hint中的提示应该有其他更效率办法，今天就先不看了，第二遍再看吧
二，C语言实现
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* struct ListNode *next;
* };
*/
struct ListNode* reverseList(struct ListNode* head) {//同样是不带头结点
struct ListNode *p,*q;
if(head==NULL || head->next==NULL)
return head;
p=head->next;
head->next=NULL;
while(p!=NULL){
q=p->next;
p->next=head;
head=p;
p=q;
}
return head;
}