Leetcode 538:Convert BST to Greater Tree

題目描述：https://leetcode.com/problems/convert-bst-to-greater-tree/#/description

解題思路：後續遍歷，每個節點的值等於其自身值加上其已經遍歷過的值之和。

AC代碼

public class Solution {
    int count = 0;
    public TreeNode convertBST(TreeNode root) {
        if(root == null) return null;
        convert(root);
        return root;
    }
    
    public void convert(TreeNode root){
        if(root == null) return;
        convert(root.right);
        count += root.val;
        root.val = count;
        convert(root.left);
    }
}