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

#define FRAGMENT_SIZE 1048576 // 1 MB in bytes
#define BUFFER_SIZE FRAGMENT_SIZE + 1

int main(int argc, char *argv[]) {
    // Check that the required arguments are provided
    if (argc != 3) {
        printf("Usage: %s file1 file2\n", argv[0]);
        return 1;
    }

    // Open the first file for reading
    FILE *file1 = fopen(argv[1], "r");
    if (!file1) {
        printf("Error opening file %s\n", argv[1]);
        return 1;
    }

    // Open the second file for reading and writing
    FILE *file2 = fopen(argv[2], "r+");
    if (!file2) {
        printf("Error opening file %s\n", argv[2]);
        return 1;
    }

    // Allocate memory for the buffer
    char *buffer1 = malloc(BUFFER_SIZE);
    char *buffer2 = malloc(BUFFER_SIZE);

    // Read one fragment from each file and compare their checksums
    while (!feof(file1) && !feof(file2)) {
        // Read one fragment from each file
        size_t bytes_read1 = fread(buffer1, 1, FRAGMENT_SIZE, file1);
        size_t bytes_read2 = fread(buffer2, 1, FRAGMENT_SIZE, file2);

        // Check if the number of bytes read is different
        if (bytes_read1 != bytes_read2) {
            printf("Error: Different number of bytes read from the files\n");
            return 1;
        }

        // Calculate the checksum of each fragment
        unsigned long checksum1 = 0;
        unsigned long checksum2 = 0;
        for (int i = 0; i < bytes_read1; i++) {
            checksum1 = checksum1 * 31 + buffer1[i];
            checksum2 = checksum2 * 31 + buffer2[i];
        }

        // Compare the checksums
        if (checksum1 != checksum2) {
            // Seek back to the start of the fragment in the second file
            if (fseek(file2, -bytes_read2, SEEK_CUR) != 0) {
                printf("Error seeking in file %s\n", argv[2]);
                return 1;
            }

            // Overwrite the fragment in the second file with the data from the first file
            if (fwrite(buffer1, 1, bytes_read1, file2) != bytes_read1) {
                printf("Error writing to file %s\n", argv[2]);
                return 1;
            }
        }
    }

    // Free the memory used for the buffers
    free(buffer1);
    free(buffer2);

    // Close the files
    fclose(file1);
    fclose(file2);


return 0;

}