合并排序C ++不排序

问题描述

我正在学习算法第一部分的课程，并且使用C ++实现了合并排序。应该执行就地排序，但不对数组进行排序。我找不到原因。希望能得到积极的回应。谢谢。

 @utils.retry(exception.SnapshotLimitReached,retries=1)
def _create_from_image(self,context,volume,image_location,image_id,image_Meta,image_service,**kwargs):
    LOG.debug("cloning %(volume_id)s from image %(image_id)s "
              " at location %(image_location)s.",{'volume_id': volume.id,'image_location': image_location,'image_id': image_id})

    virtual_size = image_Meta.get('virtual_size')
    if virtual_size:
        virtual_size = image_utils.check_virtual_size(virtual_size,volume.size,image_id)

    # Create the volume from an image.
    #
    # First see if the driver can clone the image directly.
    #
    # NOTE (singn): two params need to be returned
    # dict containing provider_location for cloned volume
    # and clone status.
    # NOTE (lixiaoy1): Currently all images are raw data,we can't
    # use clone_image to copy data if new volume is encrypted.
    volume_is_encrypted = volume.encryption_key_id is not None
    cloned = False
    model_update = None
    if not volume_is_encrypted:
        model_update,cloned = self.driver.clone_image(context,image_service)

    # Try and clone the image if we have it set as a glance location.
    if not cloned and 'cinder' in CONF.allowed_direct_url_schemes:
        model_update,cloned = self._clone_image_volume(context,image_Meta)

    # If we're going to try using the image cache then prepare the cache
    # entry. Note: encrypted volume images are not cached.
    if not cloned and self.image_volume_cache and not volume_is_encrypted:
        # If _prepare_image_cache_entry() has to create the cache entry
        # then it will also create the volume. But if the volume image
        # is already in the cache then it returns (None,False),and
        # _create_from_image_cache_or_download() will use the cache.
        model_update,cloned = self._prepare_image_cache_entry(
            context,image_service)

    # Try and use the image cache,and download if not cached.
    if not cloned:
        model_update = self._create_from_image_cache_or_download(
            context,image_service)

    self._handle_bootable_volume_glance_Meta(context,image_id=image_id,image_Meta=image_Meta)
    return model_update

void merge(int *a,int *aux,int low,int mid,int high) {
    for (int k = low; k <= high; ++k)
        aux[k] = a[k]; // copy
    int i = low,j = mid + 1;
    for (int k = low; k <= high; ++k) { // merge
        if (i > mid)
            a[k] = aux[j++];
        else if (j > mid)
            a[k] = aux[i++];
        else if (aux[i] > aux[j])
            a[k] = aux[j++];
        else
            a[k] = aux[i++];
    }
}

void sort(int *a,int high) {
    if (high <= low)
        return;
    int mid = low + (high - low) / 2;
    sort(a,aux,low,mid);
    sort(a,mid + 1,high);
    merge(a,mid,high);
}

解决方法

您的合并功能在逻辑上不正确。对于任何迭代，将永远不会执行最后两个条件。 j将始终大于mid，控制权将不会超出第二个表达式。

将合并功能的定义修改为类似这样的内容：

void merge(int *a,int *aux,int low,int mid,int high) {
    for (int k = low; k <= high; ++k)
        aux[k] = a[k]; // copy
    int i = low,j = mid + 1;
    for (int k = low; k <= high; ++k) { // merge

// changes begin here

        if (i <= mid and j <= high) {
            if (aux[i] > aux[j])
                a[k] = aux[j++];
            else
                a[k] = aux[i++];
        }
        else if (i > mid)
            a[k] = aux[j++];
        else // if (j > high)
            a[k] = aux[i++];

// changes end here

    }
}