给你单链表的头节点?head?，请你反转链表，并返回反转后的链表。
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思路一：头插
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/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* struct ListNode *next;
* };
*/
struct ListNode* reverseList(struct ListNode* head)
{
struct ListNode* newHead = NULL;
struct ListNode* cur = head;
while (cur)
{
struct ListNode* next = cur->next;
cur->next = newHead;
newHead = cur;
cur = next;
}
return newHead;
}思路二：
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struct ListNode* reverseList(struct ListNode* head)
{
if (head = NULL)
return NULL;
struct ListNode* prev = NULL;
struct ListNode* cur = head;
struct ListNode* next = head->next;
while (cur)
{
cur->next = prev;
prev = cur;
cur = next;
if(next)
next = next->next;
}
return prev;
}