Leetcode: Binary Search Tree to Greater Sum Tree

Binary Search Tree to Greater Sum Tree



Similar Problems:


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]

Binary Search Tree to Greater Sum Tree

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.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.


  • Solution:
// Blog link: https://code.dennyzhang.com/binary-search-tree-to-greater-sum-tree
// Basic Idea: tree transeveral: right, middle, left
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */

func dfs(root *TreeNode, val *int) {
        if root == nil {
                return
        }

        if root.Right != nil {
                dfs(root.Right, val)
        }

        *val += root.Val
        root.Val = *val

        if root.Left != nil {
                dfs(root.Left, val)
        }
}

func bstToGst(root *TreeNode) *TreeNode {
        val := 0
        dfs(root, &val)
        return root
}
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