//将有序子序列合并成大序列void mergeSub(int *a, int start, int middle,int end){	//申请辅助空间	int len = end - start + 1;	int *b = new int[len];	int i = start;	int j = middle + 1;	int k = 0;	while (i<=middle && j<=end)	{		b[k++] = a[i] < a[j] ? a[i++] : a[j++];	}	while (i<=middle)	{		b[k++] = a[i++];	}	while (j<=end)	{		b[k++] = a[j++];	}	for (int i = 0; i < len;i++)	{		a[start++] = b[i];	}	delete[]b;}//归并排序--递归实现（自顶向下）void mergeSort(int *a, int start,int end){	int middle = (start + end) / 2;	if (start==end)	{		return;	}	mergeSort(a, start, middle);	mergeSort(a, middle + 1, end);	mergeSub(a, start, middle, end);}//归并排序--迭代实现（自底向上）void mergeSortIterator(int *a, int start, int end){	int length = 1;   //子序列的长度	while (length