describe

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 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.

Note: This question is the same as 538: leetcode.com/problems/co…

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]Copy the code

Example 2:

Input: root = [0,null,1]
Output: [1,null,1]
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Example 3:

Input: root = [1,0,2] Output: [3, 2]Copy the code

Example 4:

Input: root = [3,2,4,1]
Output: [7,9,4,10]
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Note:

The number of nodes in the tree is in the range [1, 100].
0 <= Node.val <= 100
All the values in the tree are unique.
root is guaranteed to be a valid binary search tree.
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parsing

The sum of each node searched in the binary tree is greater than or equal to its own sum, so it is the order of the right subtree — the root node — and the left subtree to traverse all nodes, add the value traversed to the current node into sum, and assign sum to the current node.

answer

class Solution(object):
    def bstToGst(self, root):
        """
        :type root: TreeNode
        :rtype: TreeNode
        """
        def dfs(root):
            if not root:
                return
            dfs(root.right)
            self.sum += root.val
            root.val = self.sum
            dfs(root.left)
        self.sum = 0
        dfs(root)
        return root
        	      
		
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The results

Runtime: 10 ms, faster than 32.29% of Python online submissions for Binary Search Tree to Greater Sum Tree. Memory Usage: Given in Python online submissions for Binary Search Tree to Greater Sum Tree.Copy the code

Original link: leetcode.com/problems/bi…

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