c++之折半查找（二分查找）递归与非递归的实现

递归实现

template<typename T>
int binary_search2(const T arr[], const int left, const int right, const T key)
{
	if (NULL == arr || nullptr == arr || 0 > left || 0 > right)
		return -1;

	if (left > right)
		return -2;

	int mid = (left + right) / 2;
	if (0 < mid)
	{
		if (key == arr[mid])
			return mid;
		else if (key > arr[mid])
			return binary_search2(arr, mid + 1, right, key);
		else
			return binary_search2(arr, left, mid - 1, key);
	}
	// 已经越界，说明已经找不到了
	else
		return -3;
}

非递归实现

template<typename T>
int binary_search(T arr[], int len, const T find)
{

	// 参数检查
	if (0 == len || nullptr == arr || NULL == arr || 0 > len)
		return -1;

	int low = 0;
	int high = len - 1;

	while (low < high)
	{

		// 找到中间值
		int mid = (high + low) / 2;

		if (0 <= mid)
		{
			if (arr[mid] == find)
				return mid;
			else if (arr[mid] > find)
				high = mid - 1;
			else
				low = mid + 1;
		}
		else
			break;
	}

	return -2;
}