C 有没有办法使这个合并排序算法更有效？

因此，我有这个合并排序算法，我需要减少比较的数量。除了我已经拥有的数据结构之外，我不允许使用任何额外的数据结构。我完全不知道如何才能使这更有效。有人能帮忙吗

int compares = 0;

// Merge two sorted subarrays arr[low .. mid] and arr[mid + 1 .. high]
void Merge(int arr[], int aux[], int low, int mid, int high)
{
    int k = low, i = low, j = mid + 1;

    // While there are elements in the left and right runs
    while (i <= mid && j <= high)
    {
        if (arr[i] <= arr[j])
            aux[k++] = arr[i++];
            compares++;
        else
            aux[k++] = arr[j++];
    }

    // Copy remaining elements
    while (i <= mid)
        aux[k++] = arr[i++];

    // No need to copy the second half

    // copy back to the original array to reflect sorted order
    for (int i = low; i <= high; i++)
        arr[i] = aux[i];
}

// Sort array arr [low..high] using auxiliary array aux
void MergeSort(int arr[], int aux[], int low, int high)
{
    // Base case
    if (high == low)    // if run size == 1
        return;

    // find mid point
    int mid = (low + ((high - low) >> 1));

    // recursively split runs into two halves until run size == 1,
    // then merge them and return back up the call chain

    MergeSort(arr, aux, low, mid);      // split / merge left  half
    MergeSort(arr, aux, mid + 1, high); // split / merge right half

    Merge(arr, aux, low, mid, high);    // merge the two half runs
}

int=0；
//合并两个已排序的子数组arr[low..mid]和arr[mid+1..high]
无效合并（整数arr[]、整数aux[]、整数low、整数mid、整数high）
{
int k=低，i=低，j=中+1；
//而左、右梯段中都有元素
而（i您的代码中存在一些问题：


Merge
函数不正确：右数组中的剩余元素没有复制到
aux
数组，这很好（无需复制后半部分），但将元素复制回
arr
的最后一个循环应该在
i
处停止，而不是运行到
i。如果排序实际上是合并排序，则它将是O（n lg n）比较。应该减少什么“比较”？请注意
merge（）
函数不计算它执行的所有项目比较。它只在
arr[i]时更新变量
compares
，这样可以提高算法的效率（但不会减少项目比较的数量），通过避免从辅助数组复制回数据的步骤（可能在结尾处除外）。相反，从递归的底部向上提升时，在哪个数组被视为主数组和哪个辅助数组之间来回翻转。对不起，我应该澄清这一点，但我应该计算的唯一比较是数组之间的比较访问。
int compares = 0;

// Merge two sorted subarrays arr[low .. mid] and arr[mid + 1 .. high]
void Merge(int arr[], int aux[], int low, int mid, int high) {
    int k = low, i = low, j = mid + 1;

    // While there are elements in the left and right runs
    while (i <= mid && j <= high) {
        compares++;
        if (arr[i] <= arr[j])
            aux[k++] = arr[i++];
        else
            aux[k++] = arr[j++];
    }

    // Copy remaining elements
    while (i <= mid)
        aux[k++] = arr[i++];

    // No need to copy the second half

    // copy back to the original array to reflect sorted order
    for (int i = low; i < k; i++)
        arr[i] = aux[i];
}

// Sort array arr [low..high] using auxiliary array aux
void MergeSort(int arr[], int aux[], int low, int high) {
    // Base case
    if (high == low)    // if run size == 1
        return;

    // find mid point
    int mid = low + ((high - low) >> 1);

    // recursively split runs into two halves until run size == 1,
    // then merge them and return back up the call chain

    MergeSort(arr, aux, low, mid);      // split / merge left  half
    MergeSort(arr, aux, mid + 1, high); // split / merge right half

    Merge(arr, aux, low, mid, high);    // merge the two half runs
}

int compares = 0;

// Merge two sorted subarrays arr[low .. mid] and arr[mid + 1 .. high]
void Merge(int arr[], int aux[], int low, int mid, int high) {
    int k = low, i = low, j = mid + 1;

    // Extra comparison to improve special case of sorted arrays
    if (high - low > 7) {
        compares++;
        if (arr[mid] <= arr[j])
            return;
    }
    // While there are elements in the left and right runs
    while (i <= mid && j <= high) {
        compares++;
        if (arr[i] <= arr[j])
            aux[k++] = arr[i++];
        else
            aux[k++] = arr[j++];
    }

    // Copy remaining elements
    while (i <= mid)
        aux[k++] = arr[i++];

    // No need to copy the second half

    // copy back to the original array to reflect sorted order
    for (int i = low; i < k; i++)
        arr[i] = aux[i];
}