Leetcode 1114 Solution

This article provides solution to leetcode question 1114 (binary-search-tree-to-greater-sum-tree)
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https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree

Solution

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
    int s;
public:
    void doConvertBST(TreeNode* root) {
        if (root == NULL)
            return;

        doConvertBST(root->right);
        s += root->val;
        root->val = s;
        doConvertBST(root->left);
    }

    TreeNode* bstToGst(TreeNode* root) {
        s = 0;
        doConvertBST(root);
        return root;
    }
};