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 the 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.


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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]


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Constraints:


	The number of nodes in the tree is in the range [1, 100].
	0 &lt;= Node.val &lt;= 100
	All the values in the tree are unique.


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

class Solution:
    def bstToGst(self, root):
        self.total = 0
        def dfs(n):
            if n:
                dfs(n.right)
                self.total +=  n.val
                n.val       =  self.total
                dfs(n.left)
        dfs(root)
        return root
class Solution {
    int sum=0;
    public TreeNode bstToGst(TreeNode root) {
        if(root!=null){
            bstToGst(root.right);
            sum += root.val;
            root.val = sum;
            bstToGst(root.left);
        }
        return root;
    }

    
   
}
class Solution {
public:

    int s = 0;

    void solve(TreeNode* root){
        if(!root) return;
        solve(root->right);

        root->val = s + root->val;
        s = root->val;

        solve(root->left);
        return;
    }

    TreeNode* bstToGst(TreeNode* root) {
        if(!root) return NULL;
        solve(root);
        return root;
    }
};
var bstToGst = function(root) {
    let sum = 0;
    const traverse = (r = root) => {
        if(!r) return null;
        traverse(r.right);
        let temp = r.val;
        r.val += sum;
        sum += temp;
        traverse(r.left);
    }
    traverse();
    return root;
};
Binary Search Tree to Greater Sum Tree