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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:

1. The number of nodes in the tree is between 1 and 100.
2. Each node will have value between 0 and 100.
3. 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/
// Author: github.com/lzl124631x
// 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;
    }
};