Formatted question description: https://leetcode.ca/all/1038.html
1038. Binary Search Tree to Greater Sum Tree (Medium)
Given the root of a binary search tree with distinct values, modify it so that every node
has a new value equal to the sum of the values of the original tree that are greater than or equal to node.val
.
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: [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]
Note:
- The number of nodes in the tree is between
1
and100
. - Each node will have value between
0
and100
. - The given tree is a binary search tree.
Companies:
Amazon
Related Topics:
Binary Search Tree
Solution 1.
// OJ: https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree/
// Time: O(N)
// Space: O(N)
class Solution {
private:
int sum = 0;
public:
TreeNode* bstToGst(TreeNode* root) {
if (!root) return NULL;
bstToGst(root->right);
root->val = (sum += root->val);
bstToGst(root->left);
return root;
}
};
Java
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public TreeNode bstToGst(TreeNode root) {
if (root == null)
return root;
int prevVal = 0;
Stack<TreeNode> stack = new Stack<TreeNode>();
TreeNode node = root;
while (!stack.isEmpty() || node != null) {
while (node != null) {
stack.push(node);
node = node.right;
}
TreeNode visitNode = stack.pop();
visitNode.val += prevVal;
prevVal = visitNode.val;
node = visitNode.left;
}
return root;
}
}