[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.

/**
 * 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 *DFS(vector<int> &arr,int left,int right)
    {
        if(right<left) return NULL;
        int mid=(right+left)>>1;
        //每次从表头开始遍历链表寻找中间结点超时
        TreeNode *root=new TreeNode(arr[mid]);
        root->left=DFS(arr,left,mid-1);
        root->right=DFS(arr,mid+1,right);
        return root;
    }
    TreeNode *sortedListToBST(ListNode *head) {
        ListNode *p=head;
        vector<int> arr;
        while(p)
        {
            arr.push_back(p->val);
            p=p->next;
        }
        return DFS(arr,0,arr.size()-1);
    }
};