239. 滑动窗口最大值

加入时把小于val的全删除，删除时最多只删一个

class Solution {
private:
    class MyQueue {
        public:
            void push(int value)
            {
                while (que.size() && que.back() < value)
                {
                    que.pop_back();
                }
                que.push_back(value);
            }

            void pop(int value)
            {
                if (que.size() && que.front() == value)
                {
                    que.pop_front();
                }
            }

            int front()
            {
                return que.front();
            }
        private:
            deque<int> que;
    };

public:
    vector<int> maxSlidingWindow(vector<int>& nums, int k) {
        MyQueue que;
        for (int i = 0; i < k; i ++) que.push(nums[i]);
        vector<int> res;
        res.push_back(que.front());
        for (int i = k; i < nums.size(); i ++)
        {
            que.pop(nums[i-k]);
            que.push(nums[i]);
            res.push_back(que.front());
        }
        return res;
    }
};

347. 前 K 个高频元素

top k

class Solution {
public:
    vector<int> topKFrequent(vector<int>& nums, int k) {
        unordered_map<int, int> umap;
        for (int num : nums)
        {
            umap[num] ++;
        }

        priority_queue<pair<int, int>> pq;
        for (auto [x, y] : umap)
        {
            pq.push({y, x});
        }

        vector<int> res;
        while (k --)
        {
            res.push_back(pq.top().second);
            pq.pop();
        }

        return res;
    }
};