排序算法7--二路归并排序（C++完整代码实现）

#include 
using namespace std;
//归并函数
void merge(int *R, int low, int high)
{
	int mid = (low + high) / 2;
	//需要定义一个额外的数组，临时存放归并的结果
	int maxSize = high - low + 1;
	int temp[maxSize];
	int k = 0;
	int i = low;
	int j = mid + 1;
	while (i <= mid && j <= high)
	{
		if (R[i] < R[j])
			temp[k++] = R[i++];
		else
			temp[k++] = R[j++];
	}
	while (i <= mid)
		temp[k++] = R[i++];
	while (j <= high)
		temp[k++] = R[j++];
	
	//需要把临时数组里面的元素重新放回目标数组
	for (int i = low, j = 0; i <= high && j < k; ++i, ++j)
		R[i] = temp[j];
}
void mergeSort(int *R, int low, int high)
{
	if (low >= high)
		return;
	int mid = (low + high) / 2;
	mergeSort(R, low, mid);
	mergeSort(R, mid + 1, high);
	merge(R, low, high);
}

int main()
{
	int R[] = {49, 36, 24, 65, 97, 6, 25};
	int n = 7;
	mergeSort(R, 0, n-1);
	for (int i = 0; i < n; ++i)
		cout << R[i] << endl;
	return 0;
}

归并排序的时间复杂度平均情况下，最好情况下，最坏情况下均为O(nlog2n)，空间复杂度O(n)