LeetCode Convert Sorted List to Binary Search Tree

// 168ms
 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 /**
10  * Definition for binary tree
11  * struct TreeNode {
12  *     int val;
13  *     TreeNode *left;
14  *     TreeNode *right;
15  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
16  * };
17  */
18 class Solution {
19 public:
20     TreeNode *sortedListToBST(ListNode *head,int len) {
21         int mid=len/2,tem;
22         tem=mid;
23         TreeNode *root,*left,*right;
24         ListNode *p,*q,*r;
25         p=head;
26 
27         q=NULL;
28         while(tem)
29         {
30             tem--;
31             q=p;
32             p=p->next;
33         }
34         root=new TreeNode(p->val);
35 
36         if(mid)
37             root->left=sortedListToBST(head,mid);
38         if(len-mid-1)
39             root->right=sortedListToBST(p->next,len-mid-1);
40         return root;
41     }
42     TreeNode *sortedListToBST(ListNode *head) {
43         // Start typing your C/C++ solution below
44         // DO NOT write int main() function
45         ListNode *p=head;
46         if(head==NULL)
47             return NULL;
48 
49         int count=0;
50         while(p)
51         {
52             count++;
53             p=p->next;
54         }
55         return sortedListToBST(head,count);
56     }
57 };