leetcode-538. 把二叉搜索树转换为累加树

 

 

/**
 * 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:
    // 反向中序遍历
    int sum = 0;
    TreeNode* convertBST(TreeNode* root) {
        if(root==NULL)
            return NULL;

        if(root->right)
            convertBST(root->right);
        sum = sum + root->val;
        root->val = sum;
        if(root->left)
            convertBST(root->left);
        return root;
    }
};