leetcode-109-Convert Sorted List to Binary Search Tree

error:
cannot solve it.

pattern:

left open, right close for current search range
convert(head, tail):
	if(head == tail)
		return nullptr;
		
	mid = find(head, tail);
	
	TreeNode *tree_mid = new TreeNode(mid->val);
	tree_mid->left = convert(head, mid);
	tree_mid->right = convert(mid->next, tail);
	
	return mid;