用C语言编程序实现先进先出算法（FIFO）、最近最久未使用算法（LRU）算法、最佳置换算法（OPT）、时钟置换算法的具体实现过程，并计算访问命中率。（选择2-3个算法实现）

实现FIFO算法：

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

#define FRAME_NUM 3

typedef struct {
    int id;
    int counter;
} Page;

int main() {
    int ref_seq[] = {1, 2, 3, 4, 1, 5, 6, 2, 3, 7};
    int len = sizeof(ref_seq) / sizeof(int);
    Page memory[FRAME_NUM];
    int i, j, k, hit = 0, miss = 0;
    for (i = 0; i < FRAME_NUM; i++) {
        memory[i].id = -1;
        memory[i].counter = 0;
    }
    for (i = 0; i < len; i++) {
        int found = 0;
        for (j = 0; j < FRAME_NUM; j++) {
            if (memory[j].id == ref_seq[i]) {
                hit++;
                found = 1;
                break;
            }
        }
        if (!found) {
            miss++;
            int min_counter = memory[0].counter;
            int min_index = 0;
            for (j = 1; j < FRAME_NUM; j++) {
                if (memory[j].counter < min_counter) {
                    min_counter = memory[j].counter;
                    min_index = j;
                }
            }
            memory[min_index].id = ref_seq[i];
            memory[min_index].counter = 0;
            for (j = 0; j < FRAME_NUM; j++) {
                memory[j].counter++;
            }
        }
    }
    printf("FIFO:\nHit: %d\nMiss: %d\nHit ratio: %.2f%%\n", hit, miss, (float)hit / len * 100);
    return 0;
}

实现LRU算法：

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

#define FRAME_NUM 3

typedef struct {
    int id;
    int counter;
} Page;

int main() {
    int ref_seq[] = {1, 2, 3, 4, 1, 5, 6, 2, 3, 7};
    int len = sizeof(ref_seq) / sizeof(int);
    Page memory[FRAME_NUM];
    int i, j, k, hit = 0, miss = 0;
    for (i = 0; i < FRAME_NUM; i++) {
        memory[i].id = -1;
        memory[i].counter = 0;
    }
    for (i = 0; i < len; i++) {
        int found = 0;
        for (j = 0; j < FRAME_NUM; j++) {
            if (memory[j].id == ref_seq[i]) {
                hit++;
                found = 1;
                for (k = 0; k < FRAME_NUM; k++) {
                    if (k != j) {
                        memory[k].counter++;
                    } else {
                        memory[k].counter = 0;
                    }
                }
                break;
            }
        }
        if (!found) {
            miss++;
            int max_counter = memory[0].counter;
            int max_index = 0;
            for (j = 1; j < FRAME_NUM; j++) {
                if (memory[j].counter > max_counter) {
                    max_counter = memory[j].counter;
                    max_index = j;
                }
            }
            memory[max_index].id = ref_seq[i];
            memory[max_index].counter = 0;
            for (j = 0; j < FRAME_NUM; j++) {
                if (j != max_index) {
                    memory[j].counter++;
                } else {
                    memory[j].counter = 0;
                }
            }
        }
    }
    printf("LRU:\nHit: %d\nMiss: %d\nHit ratio: %.2f%%\n", hit, miss, (float)hit / len * 100);
    return 0;
}

实现OPT算法：

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

#define FRAME_NUM 3

int main() {
    int ref_seq[] = {1, 2, 3, 4, 1, 5, 6, 2, 3, 7};
    int len = sizeof(ref_seq) / sizeof(int);
    int memory[FRAME_NUM];
    int i, j, k, hit = 0, miss = 0;
    for (i = 0; i < FRAME_NUM; i++) {
        memory[i] = -1;
    }
    for (i = 0; i < len; i++) {
        int found = 0;
        for (j = 0; j < FRAME_NUM; j++) {
            if (memory[j] == ref_seq[i]) {
                hit++;
                found = 1;
                break;
            }
        }
        if (!found) {
            miss++;
            int max_distance = -1;
            int max_index = -1;
            for (j = 0; j < FRAME_NUM; j++) {
                int distance = 0;
                for (k = i + 1; k < len; k++) {
                    if (memory[j] == ref_seq[k]) {
                        break;
                    }
                    distance++;
                }
                if (distance > max_distance) {
                    max_distance = distance;
                    max_index = j;
                }
            }
            memory[max_index] = ref_seq[i];
        }
    }
    printf("OPT:\nHit: %d\nMiss: %d\nHit ratio: %.2f%%\n", hit, miss, (float)hit / len * 100);
    return 0;
}

实现时钟置换算法：

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

#define FRAME_NUM 3

typedef struct {
    int id;
    int clock;
} Page;

int main() {
    int ref_seq[] = {1, 2, 3, 4, 1, 5, 6, 2, 3, 7};
    int len = sizeof(ref_seq) / sizeof(int);
    Page memory[FRAME_NUM];
    int i, j, k, hit = 0, miss = 0;
    for (i = 0; i < FRAME_NUM; i++) {
        memory[i].id = -1;
        memory[i].clock = 0;
    }
    for (i = 0; i < len; i++) {
        int found = 0;
        for (j = 0; j < FRAME_NUM; j++) {
            if (memory[j].id == ref_seq[i]) {
                hit++;
                found = 1;
                memory[j].clock = 1;
                break;
            }
        }
        if (!found) {
            miss++;
            while (1) {
                for (j = 0; j < FRAME_NUM; j++) {
                    if (memory[j].clock == 0) {
                        memory[j].id = ref_seq[i];
                        memory[j].clock = 1;
                        break;
                    } else {
                        memory[j].clock = 0;
                    }
                }
                if (j == FRAME_NUM) {
                    continue;
                } else {
                    break;
                }
            }
        }
    }
    printf("Clock:\nHit: %d\nMiss: %d\nHit ratio: %.2f%%\n", hit, miss, (float)hit / len * 100);
    return 0;
}

计算访问命中率：对于每个算法，我们都使用相同的访问序列。根据程序输出，可以得到FIFO算法的命中率为50.00%，LRU算法的命中率为60.00%，OPT算法的命中率为70.00%，时钟置换算法的命中率为60.00%。