- 删除重复节点，只保留一个示例：Input: 1->1->2Output: 1->2代码：ListNode* deleteDuplicates(ListNode* head) { ListNode pre = head, cur = head; while (cur) { if (pre->val != cur->val) { pre->next = cur; pre = pre->next; } cur = cur->next; } if (pre) pre->next = nullptr; return head;}2. 删除全部重复节点示例：Input: 1->2->3->3->4->4->5Output: 1->2->5代码：ListNode deleteDuplicates(ListNode head) { ListNode *dummy = new ListNode(-1); dummy->next = head; ListNode *pre = dummy, *cur = head; while (cur) { while (cur->next && cur->next->val == cur->val) cur = cur->next; if (pre->next == cur) pre = cur; else pre->next = cur->next; cur = cur->next; } return dummy->next; //不能直接返回 head，因为 head 有可能被删除}