Given a sorted linked list, delete all duplicates such that each element appear only once.
For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->2->3.
设p指向当前节点，初始化为p = head, q = p->next, 则:
- 若q为null，则说明已到达尾部节点，直接返回
- 若
q->val != p->val, 更新p节点,p = p->next - 否则删除q节点，即
p->next = p->next->next; free(q)
struct ListNode* deleteDuplicates(struct ListNode *head)
{
struct ListNode *p = head;
while (p) {
struct ListNode *q = p->next;
if (q && p->val == q->val) {
p->next = p->next->next;
free(q);
} else
p = p->next;
}
return head;
}