二路并归排序算法

void mergesort(int *arr, int lo, int hi)
{
	if (hi - lo < 2) return;
	int mi = (lo + hi) / 2; 
	mergesort(arr, lo, mi);
	mergesort(arr, mi, hi);

	int templo = lo;
	int la = mi - lo; int lb = hi - mi;
	int *temp1 = new int[la];
	int *temp2 = new int[lb];
	for (int i = 0; i < la; i++)
	{
		temp1[i]=arr[i+lo]; 
	}
	for (int j = 0; j < lb; j++)
	{
		temp2[j] = arr[j + mi];
	}
	int *a=temp1, *b=temp2;
	while (a < (temp1 + la) && b < (temp2 + lb))
	{
		if (*a > *b)
		{
			arr[lo++] = *b;
			b++; 
		}
		else
		{
			arr[lo++] = *a;
			a++;
		}
	}
	if (a < (temp1 + la))
	{
		for (int i = lo; i < hi; i++)
		{
			arr[lo++] = *(a++);
		}
	}
	else if (b < (temp2 + lb))
	{
		for (int i = lo; i < hi; i++)
		{
			arr[lo++] = *(b++);
		}
	}
	lo = templo;
	delete[] temp1;
	delete[] temp2;
}