538. Convert BST to Greater Tree LeetCode Solution

In this guide, you will get 538. Convert BST to Greater Tree LeetCode Solution with the best time and space complexity. The solution to Convert BST to Greater Tree problem is provided in various programming languages like C++, Java, and Python. This will be helpful for you if you are preparing for placements, hackathons, interviews, or practice purposes. The solutions provided here are very easy to follow and include detailed explanations.

Problem Statement
Complexity Analysis
Convert BST to Greater Tree solution in C++
Convert BST to Greater Tree solution in Java
Convert BST to Greater Tree solution in Python
Additional Resources

538. Convert BST to Greater Tree LeetCode Solution image

Problem Statement of Convert BST to Greater 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 [0, 104].
-104 <= Node.val <= 104
All the values in the tree are unique.
root is guaranteed to be a valid binary search tree.

Note: This question is the same as 1038: https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree/

Complexity Analysis

Time Complexity: O(n)
Space Complexity: O(\log n)

538. Convert BST to Greater Tree LeetCode Solution in C++

class Solution {
 public:
  TreeNode* convertBST(TreeNode* root) {
    int prefix = 0;
    reversedInorder(root, prefix);
    return root;
  }

 private:
  void reversedInorder(TreeNode* root, int& prefix) {
    if (root == nullptr)
      return;

    reversedInorder(root->right, prefix);
    prefix += root->val;
    root->val = prefix;
    reversedInorder(root->left, prefix);
  }
};
/* code provided by PROGIEZ */

538. Convert BST to Greater Tree LeetCode Solution in Java

class Solution {
  public TreeNode convertBST(TreeNode root) {
    reversedInorder(root);
    return root;
  }

  private int prefix = 0;

  private void reversedInorder(TreeNode root) {
    if (root == null)
      return;

    reversedInorder(root.right);
    prefix += root.val;
    root.val = prefix;
    reversedInorder(root.left);
  }
}
// code provided by PROGIEZ

538. Convert BST to Greater Tree LeetCode Solution in Python

class Solution:
  def convertBST(self, root: TreeNode | None) -> TreeNode | None:
    prefix = 0

    def reversedInorder(root: TreeNode | None) -> None:
      nonlocal prefix
      if not root:
        return

      reversedInorder(root.right)
      prefix += root.val
      root.val = prefix
      reversedInorder(root.left)

    reversedInorder(root)
    return root
 # code by PROGIEZ