// 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 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.

//

//

// 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]

//

//

// 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.

//

// Runtime 0 ms Beats 100%

// Memory 40.3 MB Beats 58.31%

/**

* Definition for a binary tree node.

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNode right;

* TreeNode() {}

* TreeNode(int val) { this.val = val; }

* TreeNode(int val, TreeNode left, TreeNode right) {

* this.val = val;

* this.left = left;

* this.right = right;

* }

* }

*/

class Solution {

private int sum = 0;

public TreeNode bstToGst(TreeNode root) {

if (root.right != null) {

bstToGst(root.right);

}

sum = sum + root.val;

root.val = sum;

if (root.left != null) {

bstToGst(root.left);

}

return root;

}

}