108. Convert Sorted Array to Binary Search Tree

/**32ms ac * 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:    TreeNode* sortedArrayToBST(vector<int>& nums) {        if(!nums.size()) return NULL;        int len = nums.size();        TreeNode* a=new TreeNode(nums[len/2]);        vector<int> nums1;        vector<int> nums2;        nums1.insert(nums1.end(),nums.begin(),nums.begin()+len/2);        nums2.insert(nums2.end(),nums.begin()+len/2+1,nums.end());        a->left=sortedArrayToBST(nums1);        a->right=sortedArrayToBST(nums2);        return a;    }};