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程式語言 - LeetCode - C++ - 538. Convert BST to Greater Tree

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題目：


解答：

/**
 * 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 {
public:
    TreeNode* convertBST(TreeNode* root) {
        int sum = 0;

        auto dfs = [&](this auto&& dfs, TreeNode *n) {
            if (!n) {
                return;
            }

            dfs(n->right);

            sum += n->val;
            n->val = sum;

            dfs(n->left);
        };

        dfs(root);

        return root;
    }
};