leecode 206.反转链表

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1.先定义两个点，防止丢失链表，p=head, q=p
2.将head最初设为NULL
3.将指针反转，q=q->next,p->next=NULL,head=p,p=q

struct ListNode* reverseList(struct ListNode* head) {
    struct ListNode *p =head;
    struct ListNode *q = p;
    head = NULL;
    while(p!=NULL){
		q = q->next;
		p->next = head;
		head = p;
		p=q;
	}
		return head;

}

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