Leetcode•May 21, 2025

Convert BST to Greater Tree

Hazrat Ali

Leetcode

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]



Solution
/**
 * @param {TreeNode} root
 * @return {TreeNode}
 */
const convertBST = root => {
  let last = 0;

  const helper = root => {
    if (!root) {
      return null;
    }

    helper(root.right);

    root.val += last;
    last = root.val;

    helper(root.left);

    return root;
  };

  return helper(root);
};



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