Leetcode Convert Sorted List to Binary Search Tree

Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.

因为List与Array不一样，因为list只能从前往后遍历，而且不能随机访问，所以无法向Array一样使用前序遍历。因为list只能从前往后遍历，也就是升序遍历，刚好对应二叉搜树的中序遍历。

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; *//** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    ListNode* now;    TreeNode* sortedListToBST(ListNode* head) {        if(head == NULL)            return NULL;                now=head;        int count = 0;        while(now != NULL)        {            now = now->next;            count ++;        }        now = head;        return ListToBST(count);    }        TreeNode* ListToBST(int n)    {        if(n == 0)            return NULL;        TreeNode* root = new TreeNode(0);        root->left = ListToBST(n/2);        root->val = now->val;        now = now->next;        root->right = ListToBST(n-n/2-1);        return root;    }};