内排序之归并排序

内排序之归并排序

归并排序的时间复杂度为O(n logn）

template<typename E>void Merge(E *a, int p, int q, int r)
{
	int n1 = q - p + 1;
	int n2 = r - q;
	E *L = new int[n1 + 1];
	E *R = new int[n2 + 1];
	int i, j, k;

	for (i = 0; i<n1; i++) 
	{
		L[i] = a[p + i];
	}
	for (j = 0; j<n2; j++)
	 {
		R[j] = a[q + j + 1];
	}
	L[n1] = 10000000;
	R[n2] = 10000000;

	for (i = 0, j = 0, k = p; k <= r; k++)
	{
		if (L[i] <= R[j])
		{
			a[k] = L[i];
			i++;
		}
		else {
			a[k] = R[j];
			j++;
		}
	}

	delete[]L;
	delete[]R;
}

template<typename E>void Mergesort(E *a, int p, int r)
{
	if (p<r)
	{
		int q = (p + r) / 2;
		Mergesort(a, p, q);
		Mergesort(a, q + 1, r);
		Merge(a, p, q, r);
	}
}