有一个增序排列的数组，将其转换为平衡二叉搜索树。

class Node
{
	public:
		Node(int v)
		{
			value = v;
			left = NULL;
			right = NULL;
		}
	private:
		int value;
		Node *left;
		Node *right;
};

Node* sortedArrayToBST(int a[], int left, int right)
{
	if (left > right)
	{
		return NULL;
	}
	
	int mid = left + (right-left)/2;
	Node *root = new Node(a[mid]);
	root->left = sortedArrayToBST(a, left, mid-1);
	root->right = sortedArrayToBST(a, mid+1, right);
	return root;
}