Convert Sorted List to Binary Search Tree

 1 class Solution {
 2 public:
 3     TreeNode *sortedListToBST( ListNode *head ) {
 4         if( !head ) { return 0; }
 5         return ConvertSubList( head );
 6     }
 7 private:
 8     TreeNode* ConvertSubList( ListNode *node ) {
 9         if( !node ) { return 0; }
10         if( !node->next ) { return new TreeNode( node->val ); }
11         ListNode *slow = node, *fast = node->next;
12         while( fast->next ) {
13             fast = fast->next;
14             if( fast->next ) { slow = slow->next; fast = fast->next; }
15         }
16         TreeNode *treeNode = new TreeNode( slow->next->val );
17         fast = slow->next->next;
18         slow->next = 0;
19         treeNode->left = ConvertSubList( node );
20         treeNode->right = ConvertSubList( fast );
21         return treeNode;
22     }
23 };