如何用C语言实现这种外部归并排序算法？

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

// 归并两个有序数组
void merge(int arr[], int left[], int leftSize, int right[], int rightSize) {
    int i = 0, j = 0, k = 0;

    while (i < leftSize && j < rightSize) {
        if (left[i] <= right[j]) {
            arr[k++] = left[i++];
        } else {
            arr[k++] = right[j++];
        }
    }

    while (i < leftSize) {
        arr[k++] = left[i++];
    }

    while (j < rightSize) {
        arr[k++] = right[j++];
    }
}

// 外部归并排序
void externalMergeSort(int arr[], int size) {
    if (size <= 1) {
        return;
    }

    int mid = size / 2;
    int* left = (int*)malloc(mid * sizeof(int));
    int* right = (int*)malloc((size - mid) * sizeof(int));

    for (int i = 0; i < mid; i++) {
        left[i] = arr[i];
    }

    for (int i = mid; i < size; i++) {
        right[i - mid] = arr[i];
    }

    externalMergeSort(left, mid);
    externalMergeSort(right, size - mid);
    merge(arr, left, mid, right, size - mid);

    free(left);
    free(right);
}

int main() {
    int arr[] = {9, 5, 7, 2, 4, 1, 8, 3, 6};
    int size = sizeof(arr) / sizeof(arr[0]);

    externalMergeSort(arr, size);

    printf("排序结果：");
    for (int i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }

    return 0;
}