问题描述：

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

基本思想：

二分法构建二差排序树。

代码：

TreeNode *subsortedArrayToBST(vector<int > & num,int begin, int end)  //C++
    {
        if(begin == end){
            TreeNode* result = new TreeNode(num[begin]);
            return result;
        }
        
        int mid = (begin + end)/2;
        TreeNode* result = new TreeNode(num[mid]);
        
        TreeNode *left =NULL, *right = NULL;
        if(mid != begin)
            left = subsortedArrayToBST(num,begin,mid-1);
        if(mid != end)
            right = subsortedArrayToBST(num,mid+1,end);
        
        result->left = left;
        result->right = right;
        return result;
    }
    TreeNode *sortedArrayToBST(vector<int> &num) {
        if(num.size() == 0)
            return NULL;
          
        TreeNode* root = subsortedArrayToBST(num,0,num.size()-1);
        // TreeNode* root;
        return root;
    }

[leetcode]Convert Sorted Array to Binary Search Tree