538. Convert BST to Greater Tree

Posted 2020-10-11 andywu

Given a Binary Search Tree (BST), convert it to a Greater Tree such that every key of the original BST is changed to the original key plus sum of all keys greater than the original key in BST.

Example:

Input: The root of a Binary Search Tree like this:
              5
            /              2     13

Output: The root of a Greater Tree like this:
             18
            /             20     13
题目含义：：给定一棵二叉搜索树，将它转化为更大的二叉树，规则是：结点的值 = 该结点的值 + 所有比它大的结点的值的和。

 1     int sum = 0;
 2     void convert(TreeNode cur) {
 3         if (cur == null) return;
 4         convert(cur.right);
 5         sum += cur.val;
 6         cur.val = sum;
 7         convert(cur.left);
 8     }
 9     public TreeNode convertBST(TreeNode root) {
10         convert(root);
11         return root;        
12     }