[LeetCode] Convert Sorted List to Binary Search Tree

TreeNode *sortedListToBST(ListNode *head) {
	if(head == NULL) {
		return NULL;
	}
	ListNode* virtual_head = new ListNode(-1);
	virtual_head->next = head;
	ListNode *pLast = virtual_head, *pSlow = head, *pFast = head;
	while(pFast != NULL && pFast->next != NULL) {
		pLast = pLast->next;
		pSlow = pSlow->next;
		pFast = pFast->next->next;
	}
	TreeNode* root = new TreeNode(pSlow->val);
	ListNode* right_list = NULL;
	right_list = pSlow->next;
	pLast->next = NULL;
	ListNode* left_list = virtual_head->next;
	root->left = sortedListToBST(left_list);
	root->right = sortedListToBST(right_list);
	delete virtual_head;
	return root;
}