LeetCode 938. Range Sum of BST

Description

https://leetcode.com/problems/range-sum-of-bst/solution/

Given the root node of a binary search tree, return the sum of values of all nodes with a value in the range [low, high].

Example 1:

Input: root = [10,5,15,3,7,null,18], low = 7, high = 15
Output: 32

Example 2:

Input: root = [10,5,15,3,7,13,18,1,null,6], low = 6, high = 10
Output: 23

Constraints:

  • The number of nodes in the tree is in the range [1, 2 * 104].
  • 1 <= Node.val <= 105
  • 1 <= low <= high <= 105
  • All Node.val are unique.

Explanation

Depth first search to add qualified numbers to the global sum.

Python Solution

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def rangeSumBST(self, root: TreeNode, low: int, high: int) -> int:        
        self.result = 0
                
        self.helper(root, low, high)
        
        return self.result
        
    def helper(self, root, low, high):
        if not root:
            return
        
        if root.val >= low and root.val <= high:
            self.result += root.val
            

        self.helper(root.left, low, high)
        self.helper(root.right, low, high)

  • Time Complexity: O(N)
  • Space Complexity: O(N)

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