[leetcode]Convert Sorted Array to Binary Search Tree

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;    }