https://leetcode.cn/problems/remove-duplicates-from-sorted-list-ii/
删除排序链表中的重复元素 

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */

class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        if(head == nullptr || head->next == nullptr)
        {
            return head;
        }
        
        // 添加虚拟头结点
        ListNode* dummy = new ListNode();
        dummy->next = head;

        ListNode* cur = dummy;
        while(cur->next && cur->next->next)
        {
            if(cur->next->val != cur->next->next->val)
            {
                cur = cur->next;
            }
            else if(cur->next->val == cur->next->next->val)
            {
                int x = cur->next->next->val;
                ListNode* tmp = cur->next->next;
                while(tmp && x == tmp->val)
                {
                    tmp = tmp->next;
                }
                cur->next = tmp;
            }
        }

        return dummy->next;
    }
};


// class Solution {
// public:
//     ListNode* deleteDuplicates(ListNode* head) {
//         if(head == nullptr || head->next == nullptr)
//             return head;
        
//         ListNode* cur = head;

//         while(cur->next != nullptr)
//         {
//             if(cur->val != cur->next->val)
//             {
//                 cur = cur->next;
//             }
//             else if(cur->val == cur->next->val)
//             {
//                 cur->next = cur->next->next;
//                 cur = cur->next;
//             }
//         }

//         return head;
//     }
// };


https://leetcode.cn/problems/intersection-of-two-arrays/
两个数组的交集 

class Solution {
public:
    vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
        set<int> s1(nums1.begin(), nums1.end());
        set<int> s2(nums2.begin(), nums2.end());
        vector<int> result;

        for(auto e : s1)
        {
            if(s2.find(e) != s2.end())
            {
                result.push_back(e);
            }
        }

        return result;
    }
};