convert bst to greater tree

问题描述：

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。                                 

实现思路：

利用递归，左子树加上它本身和根节点和右子树的值，根节点再加上右子树的值，右子树不变。

实现代码：

/**

 * Definition of TreeNode:

 * class TreeNode {

 * public:

 *     int val;

 *     TreeNode *left, *right;

 *     TreeNode(int val) {

 *         this->val = val;

 *         this->left = this->right = NULL;

 *     }

 * }

 */

class Solution {

public:

std::vector<int> v;

    /**

     * @param root the root of binary tree

     * @return the new root

     */

    TreeNode* convertBST(TreeNode* root) {

        // Write your code here

        int sum=0;

        convert(root,sum);

        return root;

    }

    void convert(TreeNode *root,int &sum)

     {

          if(root!=NULL)

          {convert(root->right,sum);

          root->val+=sum;

          sum=root->val;

          convert(root->left,sum);

          }

     }

};

感想：

利用递归，和二叉排序树的性质