[Leetcode] convert sorted array to binary search tree

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

题意：将已排序的数组转成高度平衡的搜索二叉树。

思路：这题和Convert sorted list to binary search tree 方法一的处理方法基本一样，不同是数组可以直接访问某个元素，而链表不可以。代码如下：

/**
 * 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 *sortedArrayToBST(vector<int> &num) 
    {
        if(num.size()==0)   return NULL;
        return reBulidBST(num,0,num.size()-1);
    }
    TreeNode *reBulidBST(vector<int> &num,int beg,int end)
    {
        if(beg>end) return NULL;

        int mid=beg+(end-beg+1)/2;
        TreeNode *root=new TreeNode(num[mid]);
        root->left=reBulidBST(num,beg,mid-1);
        root->right=reBulidBST(num,mid+1,end);

        return root;
    }
};