归并排序迭代版

template<typename T>
void __Merge(T arr[], int l,int mid, int r)
{
	T* arr1 = new T[r - l + 1];
	int k = 0, i = l, j = mid + 1;
	for (; k < r - l + 1 && i<=mid &&j<=r; k++)
	{
		if (arr[i] >= arr[j])
			arr1[k] = arr[j++];
		else
			arr1[k] = arr[i++];
	}
	while(i<=mid)
		arr1[k++] = arr[i++];
	while (j <= r)
		arr1[k++] = arr[j++];
	for (int m = 0; m < r - l + 1; m++)
	{
		arr[m + l] = arr1[m];
	}
	delete[] arr1;
}

//归并排序
template<typename T>
void MergeSortBU(T arr[], int n)
{
	for (int d = 1; d <= n; d *= 2) {
		//i+d<n确保最后一次合并有2个区间
		for (int i = 0; i+d <n; i += 2*d)
		{
			//对[i,i+d-1]和[i+d,i+2d-1]区间进行合并
			if(arr[i+d-1] > arr[i+d])
				__Merge(arr, i, i + d - 1, std::min(i + 2*d - 1,n-1));
		}
	}
}

自底向上的归并排序。