学步园

递归版本

int binary_search(const int a[], int low,int up, const int key)
{
	int mid=(low+up)/2;
	if(low>up)
		return -1;
	else
	{
	if(a[mid]==key)
		return mid;
	else if(a[mid]<key)
		return binary_search(a,mid+1,up,key);
	else
		return binary_search(a,low,mid-1,key);
	}
}

非递归版本

int binary_search(const int a[], int low,int up, const int key)
{
	int mid;
	while(low<=up)
	{
		mid=(low+up)/2;
		if(a[mid]==key)
			return mid;
		else
			(a[mid]<key)?(low=mid+1):(up=mid-1);
		
	}
	return -1;
}