LeetCode Convert Sorted List to Binary Search Tree

// 168ms
 1 /**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode *sortedListToBST(ListNode *head,int len) {
        int mid=len/2,tem;
        tem=mid;
        TreeNode *root,*left,*right;
        ListNode *p,*q,*r;
        p=head;

        q=NULL;
        while(tem)
        {
            tem--;
            q=p;
            p=p->next;
        }
        root=new TreeNode(p->val);

        if(mid)
            root->left=sortedListToBST(head,mid);
        if(len-mid-1)
            root->right=sortedListToBST(p->next,len-mid-1);
        return root;
    }
    TreeNode *sortedListToBST(ListNode *head) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        ListNode *p=head;
        if(head==NULL)
            return NULL;

        int count=0;
        while(p)
        {
            count++;
            p=p->next;
        }
        return sortedListToBST(head,count);
    }
};