Day 99 of 100 Days LeetCode Challenge

LeetCode Challenge #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]



  • 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.
Video Solution
Java Solution
					class Solution {
    int sum = 0 ;
    public TreeNode bstToGst(TreeNode root) {
        return root ;

    public void helper(TreeNode root){
        if(root == null){
            return ;
        sum = sum + root.val;
        root.val = sum ;

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