# Leetcode: Binary Search Tree to Greater Sum Tree

Binary Search Tree to Greater Sum Tree Similar Problems:

Given the root of a binary search tree with distinct values, modify it so that every node has a new value equal to the sum of the values of the original tree that are greater than or equal to node.val.

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.

Example 1:

```Input: [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]
```

Note:

1. The number of nodes in the tree is between 1 and 100.
2. Each node will have value between 0 and 100.
3. The given tree is a binary search tree.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

• Solution:
```// Blog link: https://code.dennyzhang.com/binary-search-tree-to-greater-sum-tree
// Basic Idea: tree transeveral: right, middle, left
/**
* Definition for a binary tree node.
* type TreeNode struct {
*     Val int
*     Left *TreeNode
*     Right *TreeNode
* }
*/

func dfs(root *TreeNode, val *int) {
if root == nil {
return
}

if root.Right != nil {
dfs(root.Right, val)
}

*val += root.Val
root.Val = *val

if root.Left != nil {
dfs(root.Left, val)
}
}

func bstToGst(root *TreeNode) *TreeNode {
val := 0
dfs(root, &val)
return root
}
```

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