牛客网-LFU

一、题目

二、思路

1、自定义结构体存储信息，set+哈希表实现

2、set利用函数对象自定义排序规则

三、代码

struct Node
{
    int keys;
    int values;
    int val;
    int time;
};

class cmp
{
public:
    bool operator()(const Node &a, const Node &b)
    {
        if (a.val != b.val)
        {
            return a.val < b.val;
        }
        return (a.time < b.time);
    }
};

class Solution
{
public:
    /**
     * lfu design
     * @param operators int整型vector<vector<>> ops
     * @param k int整型 the k
     * @return int整型vector
     */
    vector<int> res;
    vector<int> LFU(vector<vector<int>> &operators, int k)
    {

        if (operators.empty())
        {
            return res;
        }
        size = k;
        for (int i = 0; i < operators.size(); ++i)
        {
            if (operators[i][0] == 1)
            {
                put(operators[i][1], operators[i][2]);
            }
            else if (operators[i][0] == 2)
            {
                get(operators[i][1]);
            }
        }
        return res;
    }

    int get(int key)
    {
        if (Dic.count(key) == 0)
        {
            res.emplace_back(-1);
            return -1;
        }
        Set.erase(Dic[key]);
        Dic[key].val++;
        Dic[key].time = num++;
        Set.emplace(Dic[key]);
        res.emplace_back(Dic[key].values);
        return Dic[key].values;
    }

    void put(int key, int value)
    {
        Node node;
        node.keys = key;
        node.values = value;
        node.time = num++;
        if (Dic.count(key) == 0)
        {
            node.val = 1;
            if (Set.size() < size)
            {
                Set.emplace(node);
                Dic.emplace(key, node);
                return;
            }

            Dic.erase(Set.begin()->keys);
            Set.erase(Set.begin());
            Set.emplace(node);
            Dic.emplace(key, node);
            return;
        }
        node.val = Dic[key].val + 1;
        Set.erase(Dic[key]);
        Set.emplace(node);
        Dic[key] = node;
    }

private:
    set<Node, cmp> Set;
    unordered_map<int, Node> Dic;
    int num;
    int size;
};