LintCode Convert BST to Greater Tree

1.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.

样例

Given a binary search Tree ｀{5,2,3}｀:

              5
            /   \
           2     13

Return the root of new tree

             18
            /   \
          20     13

2.分析

给定二进制搜索树（BST），将其转换为更大的树，使原始BST的每个键都更改为原始密钥

加上大于BST中原始密钥的所有键的总和。即把所有大于本身节点值的加到当前节点上。

3.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:
    /**
     * @param root the root of binary tree
     * @return the new root
     */
    void changeval(TreeNode* root, int& sum){
        if(root==NULL) return;
        changeval(root->right, sum);//首先把所有右孩子的值加到节点上
        root->val =root->val+sum;
        changeval(root->left, root->val);//把子树中左孩子的值也加到节点上
    }
    TreeNode* convertBST(TreeNode* root) {
        // Write your code here
        int sum = 0;
        changeval(root, sum);
        return root;
    }
};

4.总结

这里注意并不是单纯的把当前节点的右子树所以节点值加起来，若当前节点为双亲节点的左子树，

双亲节点的值也要加上。