LRU算法

本文主要是介绍LRU算法，对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！

 1 //QuickAccess.h
 2 
 3 #pragma once
 4 
 5 #include <map>
 6 
 7 struct QANode
 8 {
 9     QANode(int _key, int _value)
10         : key(_key)
11         , value(_value)
12         , next(nullptr)
13         , prev(nullptr) 
14     {}
15     QANode* next;
16     QANode* prev;
17     int key;
18     int value;
19 };
20 
21 class QuickAccess
22 {
23 public:
24     QuickAccess();
25 
26     QuickAccess(int size);
27 
28     ~QuickAccess();
29 
30     int Access(int id);
31 
32     double GetHitRate();
33 
34     void PrintItems();
35 
36 private:
37     void MoveToHead(QANode* hitNode);
38 
39     void InsertNode(QANode* newNode);
40 
41     int Search(int id);
42 
43 private:
44     int m_nCapacity;
45     int m_nSize = 0;
46     std::map<int, void*> m_map;
47     QANode* m_pRoot;
48 
49     int m_nAccessCount = 0;
50     int m_nHitCount = 0;
51 };

  1 //QuickAccess.cpp
  2 
  3 #include "QuickAccess.h"
  4 #include <cstdlib>
  5 #include <ctime>
  6 
  7 QuickAccess::QuickAccess()
  8     : m_nCapacity(10)
  9 {
 10     QuickAccess(m_nCapacity);
 11 }
 12 
 13 QuickAccess::QuickAccess(int nCapacity)
 14     : m_nCapacity(nCapacity)
 15 {
 16     srand(time(0));
 17     m_pRoot = new QANode(0, 0);
 18     m_pRoot->prev = m_pRoot;
 19     m_pRoot->next = m_pRoot;
 20 }
 21 
 22 QuickAccess::~QuickAccess()
 23 {
 24     QANode* currentNode = m_pRoot->next;
 25     QANode* deleteNode = currentNode;
 26     while (currentNode != m_pRoot) {
 27         currentNode = currentNode->next;
 28         delete deleteNode;
 29         deleteNode = currentNode;
 30     }
 31     delete m_pRoot;
 32     m_pRoot = nullptr;
 33 }
 34 
 35 int QuickAccess::Access(int key)
 36 {
 37     m_nAccessCount++;
 38     auto it = m_map.find(key);
 39     if (it == m_map.end()) {//未命中
 40         int value = Search(key);
 41         InsertNode(new QANode(key, value));
 42     }
 43     else {//命中
 44         m_nHitCount++;
 45         MoveToHead((QANode*)m_map[key]);
 46     }
 47     return ((QANode*)m_map[key])->value;
 48 }
 49 
 50 //1,2,3,4,5
 51 void QuickAccess::MoveToHead(QANode* hitNode)
 52 {
 53     hitNode->prev->next = hitNode->next;
 54     hitNode->next->prev = hitNode->prev;
 55 
 56     hitNode->next = m_pRoot->next;
 57     m_pRoot->next->prev = hitNode;
 58 
 59     hitNode->prev = m_pRoot;
 60     m_pRoot->next = hitNode;
 61 }
 62 
 63 void QuickAccess::InsertNode(QANode* newNode)
 64 {
 65     //insert new item to head
 66     newNode->next = m_pRoot->next;
 67     m_pRoot->next->prev = newNode;
 68     m_pRoot->next = newNode;
 69     newNode->prev = m_pRoot;
 70     m_map[newNode->key] = newNode;
 71     if (m_nSize == m_nCapacity) {//full
 72         //delete last item
 73         QANode* lastSecondItem = m_pRoot->prev->prev;
 74         m_map.erase(lastSecondItem->next->key);
 75         delete lastSecondItem->next;
 76         lastSecondItem->next = m_pRoot;
 77         m_pRoot->prev = lastSecondItem;
 78     }
 79     else {
 80         m_nSize++;
 81     }
 82 }
 83 
 84 int QuickAccess::Search(int id)
 85 {
 86     int reverse = 0;
 87     while (id) {
 88         reverse = (reverse * 10) + (id % 10);
 89         id /= 10;
 90     }
 91     return reverse;
 92 }
 93 
 94 double QuickAccess::GetHitRate()
 95 {
 96     return (m_nHitCount * 1.0) / m_nAccessCount;
 97 }
 98 
 99 void QuickAccess::PrintItems()
100 {
101     QANode* currentNode = m_pRoot->next;
102     int alignCnt = 1;
103     printf("\n******************************PrintItems*************************************\n");
104     while (currentNode != m_pRoot) {
105         printf("%d[%d]   ", currentNode->key, currentNode->value);
106         if (alignCnt % 10 == 0) {
107             printf("\n");
108             alignCnt = 0;
109         }
110         alignCnt++;
111         currentNode = currentNode->next;
112     }
113     printf("\n");
114 }

// ConsoleApplication1.cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
//

#include <iostream>
#include <random>
#include "QuickAccess.h"

void QuickAccessTest();

int main()
{
    QuickAccessTest();
    return 0;
}

void QuickAccessTest()
{
    srand(time(0));
    int cacheSize = 0;
    int searchRange = 0;
    while (1) {
        printf("input cache size and search range: ");
        if (scanf_s("%d,%d", &cacheSize, &searchRange) != 2) {
            return;
        }
        QuickAccess qa(cacheSize);
        for (int i = 0; i < 100000; i++) {
            int randValue = rand() % searchRange;
            qa.Access(randValue);
        }
        qa.PrintItems();
        printf("\nhitRate = %lf\n", qa.GetHitRate());
    }
    printf("\n\n");
}

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