# 1038. Binary Search Tree to Greater Sum Tree

Given the `root` of 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.

As a reminder, a  binary search tree  is a tree that satisfies these constraints:

• The left subtree of a node contains only nodes with keys less than the node’s key.
• The right subtree of a node contains only nodes with keys greater than the node’s key.
• Both the left and right subtrees must also be binary search trees.

Note: This question is the same as 538: https://leetcode.com/problems/convert-bst-to-greater-tree/

Example 1:

``````Input: root = [4,1,6,0,2,5,7,null,null,null,3,null,null,null,8]
Output: [30,36,21,36,35,26,15,null,null,null,33,null,null,null,8]
``````

Example 2:

``````Input: root = [0,null,1]
Output: [1,null,1]
``````

Example 3:

``````Input: root = [1,0,2]
Output: [3,3,2]
``````

Example 4:

``````Input: root = [3,2,4,1]
Output: [7,9,4,10]
``````

Constraints:

• The number of nodes in the tree is in the range `[1, 100]`.
• `0 <= Node.val <= 100`
• All the values in the tree are unique.
• `root` is guaranteed to be a valid binary search tree.

``````class Solution {
public:
TreeNode* bstToGst(TreeNode* root) {
int cur = 0;
helper(root, cur);
return root;
}
void helper(TreeNode*& node, int& cur) {
if (!node) return;
helper(node->right, cur);
node->val += cur;
cur = node->val;
helper(node->left, cur);
}
};
``````

Github 同步地址:

https://github.com/grandyang/leetcode/issues/1038

Convert BST to Greater Tree

https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree/

https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree/discuss/286725/JavaC%2B%2BPython-Revered-Inorder-Traversal