108. Convert Sorted Array to Binary Search Tree

problems:
Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

Example:

Given the sorted array: [-10,-3,0,5,9],

One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:

      0
     / \
   -3   9
   /   /
 -10  5

tips:
参考博客：https://blog.csdn.net/u012814856/article/details/77894863 二叉树中采用递归方式求解问题。
solution：

class Solution {
public:
    TreeNode* sortedArrayToBST(vector<int>& nums) 
    {
       if(!nums.size()) return NULL;
       int mid = nums.size()/2;
       TreeNode *node=new TreeNode(nums[mid]);
       vector<int> leftnode = vector<int>(nums.begin(),nums.begin()+mid);
       vector<int> rightnode = vector<int>(nums.begin()+mid+1,nums.end());
       if(mid != 0)
           node->left = sortedArrayToBST(leftnode);
        if(mid != nums.size()-1)
            node->right = sortedArrayToBST(rightnode);
        return node;
    }
};