C语言入门练习-页面置换算法实现

#include <stdio.h>
#include <stdbool.h>
#include <limits.h>
#include <stdlib.h>

typedef struct Frame
{
    int pageId;
    int visitNum;
    int accessTime;

} Frame;

// 按照访问时间先后升序
int CompareByTime(const void *a, const void *b)
{
    return ((Frame *)a)->accessTime - ((Frame *)b)->accessTime;
}

// 优先选择访问次数最少的 如果有多个 则选择最久未访问的
int CompareByVisitNumAndTime(const void *a, const void *b)
{
    Frame *frameA = (Frame *)a;
    Frame *frameB = (Frame *)b;
    int visitNumA = frameA->visitNum;
    int visitNumB = frameB->visitNum;
    if (visitNumA == visitNumB)
    {
        return frameA->accessTime - frameB->accessTime;
    }
    else
    {
        return visitNumA - visitNumB;
    }
}

int Solution(int frameNum, int windowSize, int pages[], int pagesSize)
{
    // 初始化
    Frame frames[frameNum];
    int replaceCount = 0;
    int time = 0;
    int frameSize = 0;
    for (int i = 0; i < frameNum; i++)
    {
        frames[i].pageId = -1;
        frames[i].visitNum = -1;
        frames[i].accessTime = -1;
    }
    // 遍历pages
    for (size_t i = 0; i < pagesSize; i++)
    {
        // 是否命中
        printf("The Current PageId is:%d\n", pages[i]);
        bool found = false;
        time++;
        for (size_t j = 0; j < frameNum; j++)
        {
            if (frames[j].pageId == pages[i])
            {
                // 增加访问次数和刷新时间
                frames[j].accessTime = time;
                frames[j].visitNum++;
                found = true;
                break;
            }
        }
        // 若命中 跳过这个
        if (found)
        {
            continue;
        }
        // 若未命中 需要调到内存中
        // 判断是否存在空间
        // 存在空间
        if (frameSize < frameNum)
        {
            for (size_t j = 0; j < frameNum; j++)
            {
                if (frames[j].pageId == -1)
                {
                    // 调出到页框
                    frames[j].pageId = pages[i];
                    frames[j].visitNum = 1;
                    frames[j].accessTime = time;
                    frameSize++;
                    break;
                }
            }
        }
        else
        {
            // 页面置换
            // 先按照访问时间先后，选择前windowsSize的作为候选
            // 先复制一份
            replaceCount++;
            Frame tempFrames[frameNum];
            for (size_t m = 0; m < frameNum; m++)
            {
                tempFrames[m].pageId = frames[m].pageId;
                tempFrames[m].visitNum = frames[m].visitNum;
                tempFrames[m].accessTime = frames[m].accessTime;
            }
            // 按照时间先后排序
            qsort(tempFrames, frameNum, sizeof(Frame), CompareByTime);
            // 获取前window个
            Frame windowFrames[windowSize];
            for (size_t m = 0; m < windowSize; m++)
            {
                windowFrames[m].pageId = tempFrames[m].pageId;
                windowFrames[m].visitNum = tempFrames[m].visitNum;
                windowFrames[m].accessTime = tempFrames[m].accessTime;
            }
            // 选择优先次数最少 若多个则最久未访问
            qsort(windowFrames, windowSize, sizeof(Frame), CompareByVisitNumAndTime);
            // 选择第一个置换
            int replaceId = windowFrames[0].pageId;
            printf("The replaceId is %d\n", replaceId);
            for (size_t m = 0; m < frameNum; m++)
            {
                if (frames[m].pageId == replaceId)
                {
                    frames[m].pageId = pages[i];
                    frames[m].visitNum = 1;
                    frames[m].accessTime = time;
                    break;
                }
            }
        }
    }
    return replaceCount;
}

int main()
{
    int frameNum = 4;
    int windowSize = 3;
    int pages[] = {21, 22, 23, 24, 25, 21, 22, 23, 24, 26};
    int pages_size = sizeof(pages) / sizeof(pages[0]);

    int result = Solution(frameNum, windowSize, pages, pages_size);
    printf("%d\n", result); // 输出 4

    return 0;
}

/*
注意事项：
1. qsort一定不能忘记 qsort(arr, sizeof(arr)/sizeof(arr[0]), sizeof(arr[0]),CompareFunction);
2. 注意索引的细节
3. 注意重要变量 比如frameSize一定要记得++
*/