Given a Binary Search Tree (BST), convert it to a Greater Tree such that every key of the original BST is changed to the original key plus sum of all keys greater than the original key in BST.

Example:

Input: The root of a Binary Search Tree like this:              5            /   \           2     13Output: The root of a Greater Tree like this:             18            /   \          20     13

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    void inorder(TreeNode* root){        if(root==NULL) return;        inorder(root->right);        root->val=(temp+=root->val);        inorder(root->left);    }    TreeNode* convertBST(TreeNode* root) {        inorder(root);        return root;    }private:    int temp=0;};