938 Range Sum of BST

link: Range Sum of BST

Thought

When first saw this question, I think using tree traverse could solve it and it did works.

Code

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def rangeSumBST(self, root, L, R):
        """
        :type root: TreeNode
        :type L: int
        :type R: int
        :rtype: int
        """
        self.res = 0
        def helper(root): # helper function to traverse tree
            if not root:
                return
            if L <= root.val <= R:
                self.res += root.val
                helper(root.left)
                helper(root.right)
            elif root.val < L:
                helper(root.right)
            else:
                helper(root.left)
        helper(root)
        return self.res

Runtime

Time O(n)
Space O(n)