538. Convert BST to Greater Tree
Explanation
To convert a Binary Search Tree (BST) to a Greater Tree, we can perform a reverse in-order traversal of the tree. In a reverse in-order traversal, we visit nodes in the right subtree first, followed by the current node, and then the left subtree. During this traversal, we keep track of the running sum of nodes visited so far. At each node, we update its value by adding the running sum to it.
Algorithm:
- Initialize a variable
sumto keep track of the running sum. - Perform a reverse in-order traversal of the BST.
- For each node visited:
- Update the node's value by adding
sumto it. - Update
sumby adding the node's value to it.
- Update the node's value by adding
- Return the modified root of the BST.
Time Complexity: O(n) - where n is the number of nodes in the BST. Space Complexity: O(h) - where h is the height of the BST.
class Solution {
int sum = 0;
public TreeNode convertBST(TreeNode root) {
if (root != null) {
convertBST(root.right);
sum += root.val;
root.val = sum;
convertBST(root.left);
}
return root;
}
}Code Editor (Testing phase)
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