Description

Submission

/**
 * 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* convertBST(TreeNode* root) {
        if(root == NULL) return NULL;

        convertBST(root->right);

        root->val += num;

        num = root->val;

        convertBST(root->left);

        return root;
    }
private:
    int num = 0;
};