Convert Sorted Array to Binary Search Tree转换成平衡二查搜索树

/**
 * 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 *creatTree(vector<int> &num,int left,int right){
        if(left>right)
            return NULL;
        int mid=(right+left)/2;
        TreeNode *leftNode=creatTree(num,left,mid-1);
        TreeNode *rightNode=creatTree(num,mid+1,right);
        TreeNode *node = new TreeNode(num[mid]);
        node->left=leftNode;
        node->right=rightNode;
        return node;
    }
    TreeNode *sortedArrayToBST(vector<int> &num) {
        return creatTree(num,0,num.size()-1);
    }
};