leetcode 538. Convert BST to Greater Tree 后序遍历的一个应用

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 13

Output: The root of a Greater Tree like this:
18
/ \
20 13

本题题意很简单，注意BST二叉搜索树的中序遍历得到的是一个有序序列，那么我们利用这个性质可以直接计算

代码如下：

#include <iostream>#include <vector>#include <map>#include <set>#include <queue>#include <stack>#include <string>#include <climits>#include <algorithm>#include <sstream>#include <functional>#include <bitset>#include <numeric>#include <cmath>using namespace std;/*struct TreeNode {     int val;     TreeNode *left;     TreeNode *right;     TreeNode(int x) : val(x), left(NULL), right(NULL) {}};*/class Solution {public:    int curSum = 0;    TreeNode* convertBST(TreeNode* root)    {        dfs(root);        return root;    }    void dfs(TreeNode* root)    {        if (root == NULL)            return;        else        {            dfs(root->right);            curSum += root->val;            root->val = curSum;            dfs(root->left);        }    }};