leetcode 1038. Binary Search Tree to Greater Sum Tree
题意：看题目。
代码：
/*** 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:TreeNode* bstToGst(TreeNode* root) {if(root == nullptr) return root;int sum = 0;dfs(root,sum);return root;}void dfs(TreeNode* root,int& sum){if(root == nullptr)return ;dfs(root->right,sum);sum += root->val;root->val = sum;dfs(root->left,sum);return ;}
};