Leetcode#109 Convert Sorted List to Binary Search Tree

原题地址

跟Convert Sorted Array to Binary Search Tree（参见这篇文章）类似，只不过用list就不能随机访问了。

代码：

 TreeNode *buildBST(ListNode *head, int len) {
   if (len <= )
     return NULL;

   ListNode *p = head;
   int leftLen = ;
   while (leftLen *  < len) {
     p = p->next;
     leftLen++;
   }
   TreeNode *node = new TreeNode(p->val);
   node->left = buildBST(head, leftLen - );
   node->right = buildBST(p->next, len - leftLen);

   return node;
 }

 TreeNode *sortedListToBST(ListNode *head) {
   ListNode *node = head;
   int len = ;

   while (node) {
     node = node->next;
     len++;
   }
   return buildBST(head, len);
 }